Twenty nine patients with pure dysgerminoma of the ovary were referred to the Institute of Radiology of the University of Florence between 1960 and 1983. Twenty six patients received radiation therapy after surgery; three cases, classified as Stage IA, were not submitted to postoperative radiation therapy. Five patients relapsed 2 to 16 months after initial surgery, and three of them died because of their tumours. Sites of relapse were found to be outside the treated volume in four out of these five patients. The overall survival rate for this series is 90%. The survival rate seems to depend not only on the stage of the disease, but also on initial accurate staging and appropriate therapy. Criteria for selecting patients from whom post-operative radiotherapy may be withheld are discussed.