How do I check if an item already exists in a list box, say, to prevent duplicate values? 
Keywords: ListBox Duplicate 
Posted April 13, 1996 

You will have to write a function that will loop through the list items to check for the existence of a value before adding it. The following sample should start you off:  

''' Returns the position where found (or zero if not found)
''' Can easily be changed to return true or false (As Boolean)
function IsInListBox(sItem As String, lbItems As ListBox) As Integer
dim iItem As Integer
    IsInListBox = 0
    for iItem = 1 to lbItems.Listcount
            ''' Ignore case
        if UCase$(sItem) = UCase$(lbItems.List(iItem)) then
            IsInListBox = iItem
            Exit function
        end if
    next iItem
end function