Fourteen adults and 4 children with cystic craniopharyngiomas were treated with stereotactic β-irradiation during a 6-year period. Of these patients, 10 were primary cases, and 8 were recurrences after previous major surgery. Radioactive phosphorus (32P) or yttrium (90Y) in colloidal forms were used as the radiation agents. Cyst volumes (10–130 ml) were assessed intraoperatively by the 99Tc radiodilution method. According to our treatment program, the radiation dose to the cyst wall was 20,000 rad and the total irradiation time 2 weeks. The follow-up period ranged from 1 to 6 years, with an average of 3.8 years. Postoperative shrinkage of the cysts and clinical improvement were observed in most patients. Pertinent clinical data and results of treatment are described.