In a balancing system and a method for balancing a drum of a printing plate exposer, at least one mass element is provided which can be moved substantially in the circumferential direction of the drum in order to reduce an imbalance of the drum. Previous devices and methods either needed the expertise and the knowledge of a user or external actuators which had to be driven by corresponding devices, for example computers, in order to compensate for an imbalance by moving the mass elements. The balancing system is simple and automatic balancing of the drum is achieved by a mass element being coupled to a positioning element and by its position being adjusted automatically on the basis of the circumferential extent of the printing form.