[marcoszorrilla]

Prueba este código.

Código Delphi [-]
function GridSelectAll(Grid: TDBGrid): Longint; 
begin 
  Result := 0; 
  Grid.SelectedRows.Clear; 
  with Grid.Datasource.DataSet do 
  begin 
    First; 
    DisableControls; 
    try 
      while not EOF do 
      begin 
        Grid.SelectedRows.CurrentRowSelected := True; 
        inc(Result); 
        Next; 
      end; 
    finally 
      EnableControls; 
    end; 
  end; 
end;

Un Saludo.