To reproduce: Scenario 1: - Expand RadDropDownList. - Type in a value and then select desired value with mouse. - You will see that the KeyDown event is triggered twice. Scenario 2: - Expand RadDropDownList. - Type in a value and then press Tab or Enter key. - You will see that the KeyDown event is triggered three times. Workaround: radDropDownList1.DropDownListElement.TextBox.TextBoxItem.KeyDown += TextBoxItem_KeyDown;