diff --git a/lib/csharp/src/Collections/THashSet.cs b/lib/csharp/src/Collections/THashSet.cs
new file mode 100644
index 0000000..51a09b5
--- /dev/null
+++ b/lib/csharp/src/Collections/THashSet.cs
@@ -0,0 +1,142 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Thrift.Collections
+{
+	public class THashSet<T> : ICollection<T>
+	{
+#if NET_2_0
+		TDictSet<T> set = new TDictSet<T>();
+#else
+		HashSet<T> set = new HashSet<T>();
+#endif
+		public int Count
+		{
+			get { return set.Count; }
+		}
+
+		public bool IsReadOnly
+		{
+			get { return set.IsReadOnly; }
+		}
+
+		public void Add(T item)
+		{
+			set.Add(item);
+		}
+
+		public void Clear()
+		{
+			set.Clear();
+		}
+
+		public bool Contains(T item)
+		{
+			return set.Contains(item);
+		}
+
+		public void CopyTo(T[] array, int arrayIndex)
+		{
+			set.CopyTo(array, arrayIndex);
+		}
+
+		public IEnumerator GetEnumerator()
+		{
+			return set.GetEnumerator();
+		}
+
+		IEnumerator<T> IEnumerable<T>.GetEnumerator()
+		{
+			return ((IEnumerable<T>)set).GetEnumerator();
+		}
+
+		public bool Remove(T item)
+		{
+			return set.Remove(item);
+		}
+
+#if NET_2_0
+		private class TDictSet<V> : ICollection<V>
+		{
+			Dictionary<V, TDictSet<V>> dict = new Dictionary<V, TDictSet<V>>();
+
+			public int Count
+			{
+				get { return dict.Count; }
+			}
+
+			public bool IsReadOnly
+			{
+				get { return false; }
+			}
+
+			public IEnumerator GetEnumerator()
+			{
+				return ((IEnumerable)dict.Keys).GetEnumerator();
+			}
+
+			IEnumerator<V> IEnumerable<V>.GetEnumerator()
+			{
+				return dict.Keys.GetEnumerator();
+			}
+
+			public bool Add(V item)
+			{
+				if (!dict.ContainsKey(item))
+				{
+					dict[item] = this;
+					return true;
+				}
+
+				return false;
+			}
+
+			void ICollection<V>.Add(V item)
+			{
+				Add(item);
+			}
+
+			public void Clear()
+			{
+				dict.Clear();
+			}
+
+			public bool Contains(V item)
+			{
+				return dict.ContainsKey(item);
+			}
+
+			public void CopyTo(V[] array, int arrayIndex)
+			{
+				dict.Keys.CopyTo(array, arrayIndex);
+			}
+
+			public bool Remove(V item)
+			{
+				return dict.Remove(item);
+			}
+		}
+#endif
+	}
+
+}