Function GetListIndex(oObj As Object, sValue As String) As Long
    GetListIndex = -1
    Dim i As Long
    If Not oObj Is Nothing Then
        If (TypeOf oObj Is ComboBox) Or (TypeOf  oObj Is ListBox) Then
            If oObj.ListCount > 0 Then
                For i = 0 To oObj.ListCount - 1
                    If oObj.List(i) = sValue Then GetListIndex = i: Exit For
                Next i
            End If
        End If
    End If
End Function

'   EXEMPLE  D'UTILISATION
'    =====================
Private Sub Form_Load()
    Combo1.Clear
    Combo1.AddItem "Masculin"
    Combo1.AddItem "Féminin"
    Combo1.ListIndex = GetListIndex(Combo1, "Féminin")
    
    List1.Clear
    List1.AddItem "Masculin"
    List1.AddItem "Féminin"
    List1.ListIndex = GetListIndex(List1, "Féminin")
End Sub

Private Const CB_FINDSTRING As Long = &H14C
Private Const CB_FINDSTRINGEXACT As Long = &H158
Private Const LB_FINDSTRING As Long = &H18F
Private Const LB_FINDSTRINGEXACT As Long = &H1A2
  
Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByRef lParam As Any) As Long
   
Function GetListIndex(ByRef voObj As Object, ByRef vsValue As String, Optional ByVal vbBeginsWith As Boolean = False, Optional vnStart As Long = -1) As Long
Dim eMsg As Long
   If Not voObj Is Nothing Then
       If (TypeOf voObj Is ComboBox) Then
           If vbBeginsWith Then
               eMsg = CB_FINDSTRING
           Else
               eMsg = CB_FINDSTRINGEXACT
           End If
       ElseIf (TypeOf voObj Is ListBox) Then
           If vbBeginsWith Then
               eMsg = LB_FINDSTRING
           Else
               eMsg = LB_FINDSTRINGEXACT
           End If
       Else
           Err.Raise 5
           Exit Function
       End If
   
       GetListIndex = SendMessage(voObj.hwnd, eMsg, vnStart, ByVal vsValue)
   End If
End Function 

ListBoxX.ItemIndex := ListBoxX.Items.IndexOf('un truc');
 ComboBoxX.ItemIndex := ComboBoxX.Items.IndexOf('un truc');