diff --git a/docs/API.md b/docs/API.md
index e59e75886c..a78cc5ed35 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -20,6 +20,7 @@
     - [server.onconnection(socket)](#serveronconnectionsocket)
     - [server.of(nsp)](#serverofnsp)
     - [server.close([callback])](#serverclosecallback)
+    - [server.useNamespaceValidator(fn)](#serverusenamespacevalidatorfn)
   - [Class: Namespace](#namespace)
     - [namespace.name](#namespacename)
     - [namespace.connected](#namespaceconnected)
@@ -321,6 +322,22 @@ server.listen(PORT); // PORT is free to use
 io = Server(server);
 ```
 
+#### server.useNamespaceValidator(fn)
+
+  - `fn` _(Function)_
+
+Sets up server middleware to validate whether a new namespace should be created.
+
+```js
+io.useNamespaceValidator((nsp, next) => {
+  if (nsp === 'dynamic') {
+    next(null, true);
+  } else {
+    next(new Error('Invalid namespace'));
+  }
+});
+```
+
 #### server.engine.generateId
 
 Overwrites the default method to generate your custom socket id.
diff --git a/lib/client.js b/lib/client.js
index 0b5f0446e9..adb5d20f73 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -56,17 +56,38 @@ Client.prototype.setup = function(){
  * Connects a client to a namespace.
  *
  * @param {String} name namespace
+ * @param {String} query the query parameters
  * @api private
  */
 
 Client.prototype.connect = function(name, query){
-  debug('connecting to namespace %s', name);
-  var nsp = this.server.nsps[name];
-  if (!nsp) {
-    this.packet({ type: parser.ERROR, nsp: name, data : 'Invalid namespace'});
-    return;
+  if (this.server.nsps[name]) {
+    debug('connecting to namespace %s', name);
+    return this.doConnect(name, query);
   }
 
+  this.server.checkNamespace(name, (allow) => {
+    if (allow) {
+      debug('creating namespace %s', name);
+      this.doConnect(name, query);
+    } else {
+      debug('creation of namespace %s was denied', name);
+      this.packet({ type: parser.ERROR, nsp: name, data: 'Invalid namespace' });
+    }
+  });
+};
+
+/**
+ * Connects a client to a namespace.
+ *
+ * @param {String} name namespace
+ * @param {String} query the query parameters
+ * @api private
+ */
+
+Client.prototype.doConnect = function(name, query){
+  var nsp = this.server.of(name);
+
   if ('/' != name && !this.nsps['/']) {
     this.connectBuffer.push(name);
     return;
diff --git a/lib/index.js b/lib/index.js
index 192504f77f..21cfefc9aa 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -46,6 +46,7 @@ function Server(srv, opts){
   }
   opts = opts || {};
   this.nsps = {};
+  this.nspValidators = [];
   this.path(opts.path || '/socket.io');
   this.serveClient(false !== opts.serveClient);
   this.parser = opts.parser || parser;
@@ -157,6 +158,53 @@ Server.prototype.set = function(key, val){
   return this;
 };
 
+/**
+ * Sets up server middleware to validate incoming namespaces not already created on the server.
+ *
+ * @return {Server} self
+ * @api public
+ */
+
+Server.prototype.useNamespaceValidator = function(fn){
+  this.nspValidators.push(fn);
+  return this;
+};
+
+/**
+ * Executes the middleware for an incoming namespace not already created on the server.
+ *
+ * @param name of incomming namespace
+ * @param {Function} last fn call in the middleware
+ * @api private
+ */
+
+Server.prototype.checkNamespace = function(name, fn){
+  var fns = this.nspValidators.slice(0);
+  if (!fns.length) return fn(false);
+
+  var namespaceAllowed = false; // Deny unknown namespaces by default
+
+  function run(i){
+    fns[i](name, function(err, allow){
+      // upon error, short-circuit
+      if (err) return fn(false);
+
+      // if one piece of middleware explicitly denies namespace, short-circuit
+      if (allow === false) return fn(false);
+
+      namespaceAllowed = namespaceAllowed || allow === true;
+
+      // if no middleware left, summon callback
+      if (!fns[i + 1]) return fn(namespaceAllowed);
+
+      // go on to next
+      run(i + 1);
+    });
+  }
+
+  run(0);
+};
+
 /**
  * Sets the client serving path.
  *
diff --git a/test/socket.io.js b/test/socket.io.js
index f382d503d2..ae8cdcfab8 100644
--- a/test/socket.io.js
+++ b/test/socket.io.js
@@ -878,6 +878,81 @@ describe('socket.io', function(){
         });
       });
     });
+
+    describe('dynamic', function () {
+      it('should allow connections to dynamic namespaces', function(done){
+        var srv = http();
+        var sio = io(srv);
+        srv.listen(function(){
+          var namespace = '/dynamic';
+          var dynamic = client(srv, namespace);
+          sio.useNamespaceValidator(function(nsp, next) {
+            expect(nsp).to.be(namespace);
+            next(null, true);
+          });
+          dynamic.on('error', function(err) {
+            expect().fail();
+          });
+          dynamic.on('connect', function() {
+            expect(sio.nsps[namespace]).to.be.a(Namespace);
+            expect(Object.keys(sio.nsps[namespace].sockets).length).to.be(1);
+            done();
+          });
+        });
+      });
+
+      it('should not allow connections to dynamic namespaces if not supported', function(done){
+        var srv = http();
+        var sio = io(srv);
+        srv.listen(function(){
+          var namespace = '/dynamic';
+          sio.useNamespaceValidator(function(nsp, next) {
+            expect(nsp).to.be(namespace);
+            next(null, false);
+          });
+          sio.on('connect', function(socket) {
+            if (socket.nsp.name === namespace) {
+              expect().fail();
+            }
+          });
+
+          var dynamic = client(srv,namespace);
+          dynamic.on('connect', function(){
+            expect().fail();
+          });
+          dynamic.on('error', function(err) {
+            expect(err).to.be("Invalid namespace");
+            done();
+          });
+        });
+      });
+
+      it('should not allow connections to dynamic namespaces if there is an error', function(done){
+        var srv = http();
+        var sio = io(srv);
+        srv.listen(function(){
+          var namespace = '/dynamic';
+          sio.useNamespaceValidator(function(nsp, next) {
+            expect(nsp).to.be(namespace);
+            next(new Error(), true);
+          });
+          sio.on('connect', function(socket) {
+            if (socket.nsp.name === namespace) {
+              expect().fail();
+            }
+          });
+
+          var dynamic = client(srv,namespace);
+          dynamic.on('connect', function(){
+            expect().fail();
+          });
+          dynamic.on('error', function(err) {
+            expect(err).to.be("Invalid namespace");
+            done();
+          });
+        });
+      });
+    });
   });
 
   describe('socket', function(){