Dear All,  If you are looking for close the ISDGL=1 Sharepoint dialog box on button click on C# here is the code for it Add following script files in to ascx file for open popup! <Sharepoint:ScriptLink runat="server" Name="SP.UI.Dialog.js" Localizable="false"  ID="s4" LoadAfterUI="true"/> This script will set the properties of popup window <script>     function openPop_up(pageURL, title, dlgwidth, dlgHeight) {         var options = {               url: pageURL,               title: title,             allowMaximize: false,           showClose: true,           width: dlgwidth,         height: dlgHeight,         dialogReturnValueCallback: Function.createDelegate(null, function(result, returnValue) {   ...