along the line that MelindaJohnson post,,
the subform does not have a rowsource property, it use a record source.
in the afterupdate event of the listbox, create a sring of selected items
private sub list0_afterUpdate()
dim j, sLst
with me.list0
if .itemsselected.count >0 then
for each j in .itemsselected
sLst=sLst & "," & chr(39) & .itemdata(j) & chr(39)
next
end if
sLst=mid(slst,2)
end with
me.subformname.form.recordsource="select * from tableName where [fieldname] in (" & slst & ")"
that will vary depending on the data type of the bound column of the listbox
can you post the rowsource of the listbox
also note that you have to remove the link master/child fields setting of the subform