Abstract: In general, the invention relates to wind turbines, the rotor blades of which can be adjusted in terms of their pitch angle. The invention relates in particular to an actuating drive for adjusting the pitch angle of a rotor blade of a wind turbine, comprising a large rolling bearing which comprises two bearing rings that can be rotated relative to each other, and an actuator for rotating the two bearing rings relative to each other. According to the invention, the actuating drive comprises a ring channel cylinder, which is formed in one of the bearing rings, and at least one piston, which is received in the ring channel cylinder in a movable manner and is drivingly connected to the other bearing ring of the two bearing rings.