How in the list saved? If in a table you can use this (Index is the column number of the ID in the listbox with 0 (zero) for the first column):
Dim I As Integer
With YourListBoxName
For I = 0 To .ListCount - 1
If DCount ("AnyFieldNameInTable","TableName"."IDFieldName =" & .Column(Index, I) Then .Selected(I) = True Else .Selected(I) = False
Next I