A ventilation system for a crankcase for the transport of blow-by gases from the crankcase to the intake section of an internal combustion engine with supercharger. A ventilation line reaches from the crankcase to the segment of the intake section between the supercharger and the air inlet valve. An air-oil separator is arranged in the ventilation line, as well as a return line for the return of oil separated in the air-oil separator via a tank and a tank outlet valve into the crankcase. An actuating element is arranged in or at the tank. The actuating element is charged with the pressure in the intake line behind the supercharger as working pressure and which upon sufficiently high pressure transports the oil present in the tank via the tank outlet valve into the crankcase.