Twelve years after mediastinal irradiation for Hodgkin's disease, a 38-years old man developed an infra-hisian atrioventricular block with syncopes. The rarity of this complication of radiotherapy is emphasized. A review of the literature yielded only 6 cases of atrioventricular block associated with cobalt therapy; a pathological examination was performed in two of these patients and an electrophysiological study in two others.