<script runat="server">
Sub Check(sender As Object, e As EventArgs)
   dim i
   mess.Text="<p>Selected Item(s):</p>"
   for i=0 to check1.Items.Count-1
     if check1.Items(i).Selected then
       mess.Text+=check1.Items(i).Text + "<br>"
     end if
   next
End Sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:CheckBoxList id="check1" AutoPostBack="True"
TextAlign="Right" OnSelectedIndexChanged="Check"
runat="server">
<asp:ListItem>Item 1</asp:ListItem>
<asp:ListItem>Item 2</asp:ListItem>
<asp:ListItem>Item 3</asp:ListItem>
<asp:ListItem>Item 4</asp:ListItem>
<asp:ListItem>Item 5</asp:ListItem>
<asp:ListItem>Item 6</asp:ListItem>
</asp:CheckBoxList>
<br>
<asp:label id="mess" runat="server"/>
</form>

</body>
</html>