A method for stabilizing the gain of a PET detection system with a cooling unit includes: determining the temperature of at least one component of the PET detection system, comparing the actual gain with a reference value, and actuating the cooling unit to influence the temperature such that the gain tends to the reference value. In at least one embodiment, the reference value is determined by determining the temperature of the at least one component during a test measurement, determining the gain during the test measurement, determining a functional dependence of the gain on the temperature, and selecting the reference value based on the gain to be stabilized. Advantageously, in at least one embodiment the gain can be kept constant using the described method in a simple manner, with the influence of the temperature of the components being taken into account.