Beam losses in dedicated 230-250 MeV cyclotrons for proton therapy cause radioactivity in machine parts. A systematic study has been performed of the activation of PSI’s 250 MeV SC-cyclotron for proton therapy. Since the start of the cyclotron operation dose rate measurements have been made as a function of time at several locations in and around the cyclotron. Gamma ray spectra have been measured of selected iron inserts in the pole and of copper disks in the liner of the RF system. The isotopic composition of the activation has been derived and compared with activations calculated with Monte Carlo calculations (MCNPX). The data and beam history of the cyclotron allow predictions of the dose rate during service activities shortly after beam interruption as well as after a specified period of operation.