OnClientClick event
<%@ Page Language="VB" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server"> Sub btnDelete_Click(sender AS Object, e As EventArgs) lblResult.Text = "All pages deleted!" End Sub </script> <html xmlns="http://www.w3.org/1999/xhtml" > <head id="Head1" runat="server"> <title>Button OnClientClick</title> </head> <body> <form id="form1" runat="server"> <div> <asp:Button id="btnDelete" Text="Delete Website" OnClick="btnDelete_Click" OnClientClick="return confirm('Are you sure?');" Runat="server" /> <br /><br /> <asp:Label id="lblResult" Runat="server" /> </div> </form> </body> </html>