Medulloblastomas are primitive neuroectodermal tumors that arise in the cerebella of children. Cytogenetic and loss of heterozygosity (LOH) studies have shown that deletions on the short arm of chromosome 17 occur in 25-50% of cases, suggesting that loss of a tumor suppressor gene located on 17p plays a role in the genesis or progression of medulloblastoma. We report here on an LOH analysis of 21 patients with medulloblastoma using markers for 15 polymorphic loci previously ordered on chromosome 17 by meiotic break point mapping. Although the frequency of LOH in our patients (48%) was consistent with previous reports, our maps showed much larger deletions, the smallest spanning a 38-cM genetic distance distal to marker UT49 (D17S731). Survival analysis did not show a significant association between LOH on 17p and survival, although the sample size was too small to rule out a difference of less than 10-fold. Clinical risk factors were better prognostic indicators than LOH, with significantly prolonged survival in patients free of craniospinal metastasis following gross total tumor resection.