[dec]

Hola,

Código Delphi [-]
 procedure TForm1.Button1Click(Sender: TObject);
 var
   i: integer;
   total: integer;
 begin
   total := 0;
   for i := 0 to ListBox1.Count-1 do
   begin
     if ListBox1.Selected[i] then
       Inc(total);
   end;
   ShowMessage(IntToStr(total));
 end;