diff --git a/README.md b/README.md
index 8e3b918..7104374 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,7 @@ The package defines these formats:
 - _ipv4_: IP address v4.
 - _ipv6_: IP address v6.
 - _regex_: tests whether a string is a valid regular expression by passing it to RegExp constructor.
+- _ulid_: Universally Unique Lexicographically Sortable Identifier according to [GitHub ulid/spec](https://github.com/ulid/spec)
 - _uuid_: Universally Unique IDentifier according to [RFC4122](http://tools.ietf.org/html/rfc4122).
 - _json-pointer_: JSON-pointer according to [RFC6901](https://tools.ietf.org/html/rfc6901).
 - _relative-json-pointer_: relative JSON-pointer according to [this draft](http://tools.ietf.org/html/draft-luff-relative-json-pointer-00).
diff --git a/src/formats.ts b/src/formats.ts
index d3cde9b..922111b 100644
--- a/src/formats.ts
+++ b/src/formats.ts
@@ -19,6 +19,7 @@ export type FormatName =
   | "ipv4"
   | "ipv6"
   | "regex"
+  | "ulid"
   | "uuid"
   | "json-pointer"
   | "json-pointer-uri-fragment"
@@ -69,6 +70,8 @@ export const fullFormats: DefinedFormats = {
   ipv4: /^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$/,
   ipv6: /^((([0-9a-f]{1,4}:){7}([0-9a-f]{1,4}|:))|(([0-9a-f]{1,4}:){6}(:[0-9a-f]{1,4}|((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9a-f]{1,4}:){5}(((:[0-9a-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9a-f]{1,4}:){4}(((:[0-9a-f]{1,4}){1,3})|((:[0-9a-f]{1,4})?:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9a-f]{1,4}:){3}(((:[0-9a-f]{1,4}){1,4})|((:[0-9a-f]{1,4}){0,2}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9a-f]{1,4}:){2}(((:[0-9a-f]{1,4}){1,5})|((:[0-9a-f]{1,4}){0,3}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9a-f]{1,4}:){1}(((:[0-9a-f]{1,4}){1,6})|((:[0-9a-f]{1,4}){0,4}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(:(((:[0-9a-f]{1,4}){1,7})|((:[0-9a-f]{1,4}){0,5}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:)))$/i,
   regex,
+  // ulid: https://github.com/ulid/spec
+  ulid: /^[0-7][0-9A-HJKMNP-TV-Z]{25}$/,
   // uuid: http://tools.ietf.org/html/rfc4122
   uuid: /^(?:urn:uuid:)?[0-9a-f]{8}-(?:[0-9a-f]{4}-){3}[0-9a-f]{12}$/i,
   // JSON-pointer: https://tools.ietf.org/html/rfc6901
diff --git a/tests/extras/format.json b/tests/extras/format.json
index 1a72ec4..5d6d480 100644
--- a/tests/extras/format.json
+++ b/tests/extras/format.json
@@ -600,6 +600,47 @@
       }
     ]
   },
+  {
+    "description": "validation of ulid strings",
+    "schema": {"format": "ulid"},
+    "tests": [
+      {
+        "description": "a valid ulid",
+        "data": "01ARZ3NDEKTSV4RRFFQ69G5FAV",
+        "valid": true
+      },
+      {
+        "description": "not valid ulid as it is too long",
+        "data": "01ARZ3NDEKTSV4RRFFQ69G5FAVA",
+        "valid": false
+      },
+      {
+        "description": "not valid ulid as it is too short",
+        "data": "01ARZ3NDEKTSV4RRFFQ69G5FA",
+        "valid": false
+      },
+      {
+        "description": "not valid ulid as it has a lower case character",
+        "data": "01ARZ3NDEKTSV4rRFFQ69G5FAV",
+        "valid": false
+      },
+      {
+        "description": "not valid ulid as it has a hyphen",
+        "data": "01ARZ3NDEKTSV4-RFFQ69G5FAV",
+        "valid": false
+      },
+      {
+        "description": "not valid ulid as it starts with an 8",
+        "data": "81ARZ3NDEKTSV4RRFIQ69G5FAV",
+        "valid": false
+      },
+      {
+        "description": "not valid ulid as it has an I",
+        "data": "01ARZ3NDEKTSV4IRFIQ69G5FAV",
+        "valid": false
+      }
+    ]
+  },
   {
     "description": "validation of uuid strings",
     "schema": {"format": "uuid"},