Hi Claudio ,

If you have an accordion extender by the name "Accordion1" , you will have  a Hidden Value stored on the page called as

"Accordion1_AccordionExtender_ClientState" which stores the SelectedIndex of the Accordion.

Hope this Helps

Can we go back to this in more details. For example I have page with a DropDownList and Accordion with three panes sitting inside ModalPopupExtender and depending on the value selected from the list I need to popup a modal with a specific pane open. How do I achive this?

Thanks.

I think THis Thread should address your issue

http://forums.asp.net/thread/1601837.aspx