In a method for determining the direction of rotation of a drive shaft (13) of an internal combustion engine (1) without using a sensor specifically provided therefor, an operating variable of the internal combustion engine (1) is measured using a sensor in a gas line (40, 16), which connects a combustion chamber (30) of the internal combustion engine (1) to the surrounding area. The operating variable is calculated using a model. A forward direction of rotation of the drive shaft (13) is detected if the difference between the measured value of the operating variable and the model value of the operating variable lies within a specified tolerance range. Otherwise, a reverse direction of rotation of the drive shaft (13) is detected, which is opposite of the forward direction of rotation.