Hi Nico,
Thanks for the response. I get the idea, and have downloaded and looked at your code (which I may use elsewhere!) but I'm not sure as I can get this to practically work for my requirements. What I am after is similar to Excel where you have the "quick sum" ability in the bottom right hand corner in the status bar. You can easily and quickly hold down control/Shift and select multiple non-adjacent cells and see the sum...

I have an unbound listbox (list1) on my form.
Another unbound listbox (list2) that shows the totals of the values in the months in (list1)
I am trying to add a third listbox (list3) that subtotals the selected items in (list1)

I have multi-select set to extended to allow the multiselection.

I suspect I need to code something with the listindex and itemsselected?

Was hoping to copy (list2)...