In a method for operating an internal combustion engine with a crankcase breather venting into an intake tract, operating parameters of the internal combustion engine are measured 102. A mass flow of fuel from the crankcase into the intake tract is determined as a function of the operating parameters measured 103. The internal combustion engine is controlled 111 or monitored 108 as a function of the mass flow of fuel from the crankcase into the intake tract.