Seventeen adult patients with medulloblastoma were treated at Rush-Presbyterian-St. Luke's Medical Center and affiliated hospital between 1969 and 1986. All patients had a surgical procedure (total excision in seven patients, partial resection in nine patients, and biopsy alone in one patient) followed by radiation therapy to the craniospinal axis. The 5-year actuarial survival rate is 77% with a disease-free survival of 58%. Five patients have relapsed in the posterior fossa, one in the brain parenchyma, and two in osseous sites. Two of the local relapses occurred more than 4 years after initial treatment. Patients undergoing "total" resection of the tumor fared better than those with partial resection or biopsy only. Local failure was uncommon with posterior fossa doses greater than 55 Gy, and there was a trend toward better local control when the radiation therapy was completed in less than 7 weeks. The histologic indicators of poor outcome were necrosis, high mitotic index, and "classical" histologic appearance.