A method and a control device are for controlling the temperature of a detector system inside a computed tomography unit. The CT unit includes a rotatable gantry with a gantry housing in which both an X-ray tube and the detector system are located. The detector system is arranged, in turn, inside a detector housing. The air temperature is set in the gantry housing via a temperature-controlled air circulation. The temperature of the ambient air of the detector housing is set by a control system that uses the temperature of the detector system as controlled variable.