The Centro Nazionale di Adroterapia Oncologica (CNAO) of Pavia is the only Italian structure capable of administering therapeutic radiotherapy treatments with heavy particles (carbon ions, protons) accelerated; in addition to this, it hosts significant research activity, both as basic research and for health-related applications. From the perspective of radioprotection, the most significant risk profile is that linked to external irradiation, from three categories of sources: accelerated external beams (in addition to the treatment beams there are conventional linear accelerators), materials activated following irradiation during treatment or during research activities, unstable isotopes used for diagnostic purposes. The CNAO building has been designed and built to guarantee maximum safety both to the operator and to the patient or visitor, with widely redundant systems in order to exclude the occurrence of accidental irradiation, and to minimize the risk of exposure to activated materials. The cohort of workers shows "atypical" characteristics for healthcare safacilities due to the absolute disproportion between classified and unclassified personnel, the homogeneity of training paths, and demographic characteristics. The health surveillance of the exposed, all classified in category B pursuant to Legislative Decree 230/95, is based on the adoption of the AIRM Protocol, tempered on the specific characteristics of the work process. The main critical issues related to the health surveillance of the exposed CNAO workers come from the energies used, with significant activation capacity, and from the presence of personnel in training.