diff --git a/HISTORY.md b/HISTORY.md
index f84adb5b..54eafdab 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -4,6 +4,9 @@ http://visjs.org
 
 ## not yet released, version 3.9.2-SNAPSHOT
 
+### DataSet
+
+- Added property `length` holding the total number of items in the DataSet.
 
 
 ## 2015-01-16, version 3.9.1
diff --git a/docs/dataset.html b/docs/dataset.html
index d6c2bf81..110afc0a 100644
--- a/docs/dataset.html
+++ b/docs/dataset.html
@@ -21,6 +21,7 @@
   <li><a href="#Example">Example</a></li>
   <li><a href="#Construction">Construction</a></li>
   <li><a href="#Methods">Methods</a></li>
+  <li><a href="#Properties">Properties</a></li>
   <li><a href="#Subscriptions">Subscriptions</a></li>
   <li><a href="#Data_Manipulation">Data Manipulation</a></li>
   <li><a href="#Data_Selection">Data Selection</a></li>
@@ -373,6 +374,29 @@ var data = new vis.DataSet([data] [, options])
 </table>
 
 
+<h2 id="Properties">Properties</h2>
+
+<p>DataSet contains the following properties.</p>
+
+<table>
+  <colgroup>
+    <col width="200">
+  </colgroup>
+
+  <tr>
+    <th>Property</th>
+    <th>Type</th>
+    <th>Description</th>
+  </tr>
+
+  <tr>
+    <td>length</td>
+    <td>Number</td>
+    <td>The number of items in the DataSet.</td>
+  </tr>
+</table>
+
+
 <h2 id="Subscriptions">Subscriptions</h2>
 
 <p>
diff --git a/lib/DataSet.js b/lib/DataSet.js
index f1f3b67a..975f40de 100644
--- a/lib/DataSet.js
+++ b/lib/DataSet.js
@@ -53,6 +53,7 @@ function DataSet (data, options) {
 
   this._options = options || {};
   this._data = {};                                 // map with data indexed by id
+  this.length = 0;                                 // number of items in the DataSet
   this._fieldId = this._options.fieldId || 'id';   // name of the field containing id
   this._type = {};                                 // internal field types (NOTE: this can differ from this._options.type)
 
@@ -737,6 +738,7 @@ DataSet.prototype._remove = function (id) {
   if (util.isNumber(id) || util.isString(id)) {
     if (this._data[id]) {
       delete this._data[id];
+      this.length--;
       return id;
     }
   }
@@ -744,6 +746,7 @@ DataSet.prototype._remove = function (id) {
     var itemId = id[this._fieldId];
     if (itemId && this._data[itemId]) {
       delete this._data[itemId];
+      this.length--;
       return itemId;
     }
   }
@@ -759,6 +762,7 @@ DataSet.prototype.clear = function (senderId) {
   var ids = Object.keys(this._data);
 
   this._data = {};
+  this.length = 0;
 
   this._trigger('remove', {items: ids}, senderId);
 
@@ -884,6 +888,7 @@ DataSet.prototype._addItem = function (item) {
     }
   }
   this._data[id] = d;
+  this.length++;
 
   return id;
 };
diff --git a/test/DataSet.test.js b/test/DataSet.test.js
index 85f8e455..0def1526 100644
--- a/test/DataSet.test.js
+++ b/test/DataSet.test.js
@@ -26,6 +26,7 @@ describe('DataSet', function () {
     ]);
 
     var items = data.get();
+    assert.equal(data.length, 4);
     assert.equal(items.length, 4);
     items.forEach(function (item) {
       assert.ok(item.start instanceof Date);
@@ -76,6 +77,7 @@ describe('DataSet', function () {
       {id: 3},
       {id: 4}
     ]);
+    assert.equal(data.length, 3);
 
     // add an item
     data.add({id: 5, content: 'Item 5', start: now.valueOf()});
@@ -87,12 +89,17 @@ describe('DataSet', function () {
       {id: 4},
       {id: 5}
     ]);
+    assert.equal(data.length, 4);
 
     // update an item
     data.update({id: 5, content: 'changed!'});                         // update item (extend existing fields)
+    assert.equal(data.length, 4);
     data.remove(3);                                                    // remove existing item
+    assert.equal(data.length, 3);
     data.add({id: 3, other: 'bla'});                                   // add new item
+    assert.equal(data.length, 4);
     data.update({id: 6, content: 'created!', start: now.valueOf()});   // this item is not yet existing, create it
+    assert.equal(data.length, 5);
     assert.deepEqual(data.get().sort(sort), [
       {id: 1, content: 'Item 1', start: now},
       {id: 3, other: 'bla'},
@@ -100,8 +107,10 @@ describe('DataSet', function () {
       {id: 5, content: 'changed!', start: now},
       {id: 6, content: 'created!', start: now}
     ]);
+    assert.equal(data.length, 5);
 
     data.clear();
+    assert.equal(data.length, 0);
 
     assert.equal(data.get().length, 0);