A gasket for a valve in an internal combustion engine is provided with a first elastically deformable portion adapted to cooperate with a rod of the valve. A second elastically deformable portion is adapted to cooperate with an outer surface of a guide element of the valve, and a third elastically deformable portion is interposed between the first and the second elastically deformable portions and bearing a cantilevered gas tight seal lip is adapted to cooperate with the rod of the valve. The lip displays a frustoconical configuration with a section decreasing in opposite direction to the pressure forces directed towards the first elastically deformable portion and is connected to the third elastically deformable portion at its greater section part. The lip is further connected on the side exposed to the pressure forces, to the third elastically deformable portion by a surface bearing one or more waves.