or
listbox.get_selectedItem();in a multi select listbox gets the first selected, not the "last selected".
function onSelectedIndexChanged(sender, args) { var listbox = $find("<%= MyListBox.ClientID %>"); var items = listbox.get_selectedItems(); if (items.length > 5) { // var item = get last selected item ?? listbox.trackChanges(); listbox.get_items().remove(item); listbox.commitChanges(); }