Fifty-two newly diagnosed patients with medulloblastoma were prospectively staged with myelography. Fifty also had at least one CSF cytology study. Twenty-four patients (46%) had evidence of dissemination beyond the posterior fossa at diagnosis. Patients under age 5 years were more likely to have dissemination at diagnosis than older patients (61% vs 38%). The 5-year disease-free survival for 45 patients diagnosed at least 1 year ago and treated with craniospinal irradiation was 62.6%. Overall 5-year survival for this group was 76.7%. Patients without evidence of dissemination at diagnosis had a 5-year disease-free survival of 73.3% compared to 49.1% for patients with M1-3 disease. Eighteen patients relapsed, 16 within 3 years of diagnosis. Eight patients had recurrent tumor in the posterior fossa, eight in the supratentorial compartment, seven in the cord, and five had systemic metastasis. Patients with initial cord involvement were more likely to develop systemic metastasis (4/12) than patients without initial cord involvement (1/33).