diff --git a/typed-racket-doc/typed-racket/scribblings/reference/special-forms.scrbl b/typed-racket-doc/typed-racket/scribblings/reference/special-forms.scrbl
index aa676217..df5145b2 100644
--- a/typed-racket-doc/typed-racket/scribblings/reference/special-forms.scrbl
+++ b/typed-racket-doc/typed-racket/scribblings/reference/special-forms.scrbl
@@ -465,6 +465,25 @@ the type:
     (define-type Bar (U Bar False))]
 }
 
+@section{Defining New Subtypes}
+
+@defform[(define-new-subtype name (constructor t))]{
+Defines a new type @racket[name] that is a subtype of @racket[t].
+The @racket[constructor] is defined as a function that takes a value of type
+@racket[t] and produces a value of the new type @racket[name].
+A @racket[define-new-subtype] definition is only allowed at the top level of a
+file or module.
+@ex[(module m typed/racket
+      (provide Radians radians f)
+      (define-new-subtype Radians (radians Real))
+      (: f : [Radians -> Real])
+      (define (f a)
+        (sin a)))
+    (require 'm)
+    (radians 0)
+    (f (radians 0))]
+}
+
 @section{Generating Predicates Automatically}
 
 @defform[(make-predicate t)]{
diff --git a/typed-racket-lib/typed-racket/base-env/prims-struct.rkt b/typed-racket-lib/typed-racket/base-env/prims-struct.rkt
index 9b3973e4..49037590 100644
--- a/typed-racket-lib/typed-racket/base-env/prims-struct.rkt
+++ b/typed-racket-lib/typed-racket/base-env/prims-struct.rkt
@@ -29,7 +29,8 @@
 (begin-for-syntax
   (lazy-require [syntax/struct (build-struct-names)]))
 
-(provide define-typed-struct -struct define-typed-struct/exec define-type-alias dtsi* dtsi/exec*)
+(provide define-typed-struct -struct define-typed-struct/exec dtsi* dtsi/exec*
+         define-type-alias define-new-subtype)
 
 (define-for-syntax (with-type* expr ty)
   (with-type #`(ann #,expr #,ty)))
@@ -209,3 +210,27 @@
                #'(begin))
          #,(internal (syntax/loc stx
                        (define-type-alias-internal tname type poly-vars))))]))
+
+(define-syntax define-new-subtype
+  (lambda (stx)
+    (unless (memq (syntax-local-context) '(module module-begin))
+      (raise-syntax-error 'define-new-subtype
+                          "can only be used at module top-level"))
+    (syntax-parse stx
+      [(define-new-subtype ty:id (constructor:id rep-ty:expr))
+       #:with gen-id (generate-temporary #'ty)
+       #:with stx-err-fun
+       #'(lambda (stx)
+           (raise-syntax-error
+            'type-check
+            "type name used out of context"
+            stx
+            (and (stx-pair? stx) (stx-car stx))))
+       #`(begin
+           #,(ignore
+              #'(begin
+                  (define-syntax ty stx-err-fun)
+                  (define constructor (lambda (x) x))))
+           #,(internal (syntax/loc stx
+                         (define-new-subtype-internal ty (constructor rep-ty) #:gen-id gen-id))))])))
+
diff --git a/typed-racket-lib/typed-racket/base-env/prims.rkt b/typed-racket-lib/typed-racket/base-env/prims.rkt
index f6fec418..6cd6f35f 100644
--- a/typed-racket-lib/typed-racket/base-env/prims.rkt
+++ b/typed-racket-lib/typed-racket/base-env/prims.rkt
@@ -39,6 +39,7 @@ the typed racket language.
          (all-from-out "case-lambda.rkt")
          (all-from-out (submod "prims-contract.rkt" forms))
          define-type-alias
+         define-new-subtype
          define-typed-struct
          define-typed-struct/exec
          ann inst
diff --git a/typed-racket-lib/typed-racket/private/type-contract.rkt b/typed-racket-lib/typed-racket/private/type-contract.rkt
index 1609ae74..c8fb942e 100644
--- a/typed-racket-lib/typed-racket/private/type-contract.rkt
+++ b/typed-racket-lib/typed-racket/private/type-contract.rkt
@@ -351,6 +351,8 @@
          (listof/sc (t->sc elem-ty))]
         [(Base: sym cnt _ _)
          (flat/sc #`(flat-named-contract '#,sym (flat-contract-predicate #,cnt)) sym)]
+        [(Distinction: _ _ t) ; from define-new-subtype
+         (t->sc t)]
         [(Refinement: par p?)
          (and/sc (t->sc par) (flat/sc p?))]
         [(Union: elems)
diff --git a/typed-racket-lib/typed-racket/rep/type-rep.rkt b/typed-racket-lib/typed-racket/rep/type-rep.rkt
index 90c3fa71..7ae70e1a 100644
--- a/typed-racket-lib/typed-racket/rep/type-rep.rkt
+++ b/typed-racket-lib/typed-racket/rep/type-rep.rkt
@@ -579,6 +579,17 @@
   [#:frees (λ (f) (make-invariant (f value)))]
   [#:key 'continuation-mark-key])
 
+;; Distinction
+;; comes from define-new-subtype
+;; nm: a symbol representing the name of the type
+;; id: a symbol created with gensym
+;; ty: a type for the representation, where this will be a subtype of ty
+(def-type Distinction ([nm symbol?] [id symbol?] [ty Type/c])
+  [#:frees (λ (f) (f ty))]
+  [#:intern (list (Rep-seq ty) nm id)]
+  [#:fold-rhs (*Distinction nm id (type-rec-id ty))]
+  [#:key (Type-key ty)])
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 ;; remove-dups: List[Type] -> List[Type]
diff --git a/typed-racket-lib/typed-racket/typecheck/internal-forms.rkt b/typed-racket-lib/typed-racket/typecheck/internal-forms.rkt
index db833499..54bc20b6 100644
--- a/typed-racket-lib/typed-racket/typecheck/internal-forms.rkt
+++ b/typed-racket-lib/typed-racket/typecheck/internal-forms.rkt
@@ -21,6 +21,7 @@
   internal
 
   type-alias
+  new-subtype-def
   type-refinement
   typed-struct
   typed-struct/exec
@@ -31,6 +32,7 @@
   typecheck-failure
 
   type-alias?
+  new-subtype-def?
   typed-struct?
   typed-struct/exec?)
 
@@ -50,6 +52,7 @@
   (internal-forms internal-literals
                   require/typed-internal
                   define-type-alias-internal
+                  define-new-subtype-internal
                   define-type-internal
                   define-typed-struct-internal
                   define-typed-struct/exec-internal
@@ -127,6 +130,8 @@
 (define-internal-classes
   [type-alias
     (define-type-alias-internal name type args)]
+  [new-subtype-def
+    (define-new-subtype-internal name (constructor rep-type) #:gen-id gen-id)]
   [type-refinement
     (declare-refinement-internal predicate)]
   [typed-struct
diff --git a/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt b/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt
index 3421fa41..e4888a20 100644
--- a/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt
+++ b/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt
@@ -67,6 +67,17 @@
       [_:type-alias
        (list)]
 
+      ;; define-new-subtype
+      [form:new-subtype-def
+       ;; (define-new-subtype-internal name (constructor rep-type) #:gen-id gen-id)
+       (define name (syntax-e (attribute form.name)))
+       (define sym (syntax-e (attribute form.gen-id)))
+       (define rep-ty (parse-type (attribute form.rep-type)))
+       (define new-ty (-Distinction name sym rep-ty))
+       (register-type (attribute form.constructor) (-> rep-ty new-ty))
+       (register-type-alias (attribute form.name) new-ty)
+       (list)]
+
       ;; declare-refinement
       ;; FIXME - this sucks and should die
       [t:type-refinement
diff --git a/typed-racket-lib/typed-racket/types/abbrev.rkt b/typed-racket-lib/typed-racket/types/abbrev.rkt
index 82d959d3..563c38e8 100644
--- a/typed-racket-lib/typed-racket/types/abbrev.rkt
+++ b/typed-racket-lib/typed-racket/types/abbrev.rkt
@@ -286,6 +286,10 @@
 (define-syntax-rule (->opt args ... [opt ...] res)
   (opt-fn (list args ...) (list opt ...) res))
 
+;; from define-new-subtype
+(define (-Distinction name sym ty)
+  (make-Distinction name sym ty))
+
 ;; class utilities
 
 (begin-for-syntax
diff --git a/typed-racket-lib/typed-racket/types/printer.rkt b/typed-racket-lib/typed-racket/types/printer.rkt
index cf33d91b..c91c09be 100644
--- a/typed-racket-lib/typed-racket/types/printer.rkt
+++ b/typed-racket-lib/typed-racket/types/printer.rkt
@@ -517,6 +517,8 @@
      `(Sequenceof ,@(map t->s ts))]
     [(Error:) 'Error]
     [(fld: t a m) `(fld ,(type->sexp t))]
+    [(Distinction: name sym ty) ; from define-new-subtype
+     name]
     [else `(Unknown Type: ,(struct->vector type))]
     ))
 
diff --git a/typed-racket-lib/typed-racket/types/subtype.rkt b/typed-racket-lib/typed-racket/types/subtype.rkt
index b3cb9cb7..e6f24906 100644
--- a/typed-racket-lib/typed-racket/types/subtype.rkt
+++ b/typed-racket-lib/typed-racket/types/subtype.rkt
@@ -292,6 +292,9 @@
           #f]
          [((or (? Struct? s1) (NameStruct: s1)) (Value: (? (negate struct?) _)))
           #f]
+         ;; from define-new-subtype
+         [((Distinction: _ _ t1) t2)
+          (subtype* A0 t1 t2)]
          ;; sequences are covariant
          [((Sequence: ts) (Sequence: ts*))
           (subtypes* A0 ts ts*)]
diff --git a/typed-racket-test/fail/define-new-subtype.rkt b/typed-racket-test/fail/define-new-subtype.rkt
new file mode 100644
index 00000000..4c5d8375
--- /dev/null
+++ b/typed-racket-test/fail/define-new-subtype.rkt
@@ -0,0 +1,5 @@
+#lang typed/racket/base
+
+(require "../succeed/define-new-subtype.rkt")
+
+(sin (degrees 0))
diff --git a/typed-racket-test/succeed/define-new-subtype.rkt b/typed-racket-test/succeed/define-new-subtype.rkt
new file mode 100644
index 00000000..3bab1d6d
--- /dev/null
+++ b/typed-racket-test/succeed/define-new-subtype.rkt
@@ -0,0 +1,35 @@
+#lang typed/racket/base
+
+(provide Radians Degrees radians degrees
+         sin cos tan asin acos atan
+         degrees->radians radians->degrees
+         )
+
+(require (prefix-in rkt: (combine-in typed/racket/base racket/math)))
+
+(define-new-subtype Radians (radians Real))
+(define-new-subtype Degrees (degrees Real))
+
+(: sin : Radians -> Real)
+(: cos : Radians -> Real)
+(: tan : Radians -> Real)
+(define (sin x) (rkt:sin x))
+(define (cos x) (rkt:sin x))
+(define (tan x) (rkt:tan x))
+(: asin : Real -> Radians)
+(: acos : Real -> Radians)
+(: atan : Real -> Radians)
+(define (asin x) (radians (rkt:asin x)))
+(define (acos x) (radians (rkt:acos x)))
+(define (atan x) (radians (rkt:atan x)))
+
+(: degrees->radians : Degrees -> Radians)
+(: radians->degrees : Radians -> Degrees)
+(define (degrees->radians x)
+  (radians (rkt:degrees->radians x)))
+(define (radians->degrees x)
+  (degrees (rkt:radians->degrees x)))
+
+(void
+ (sin (asin 1/2))
+ )