We have reviewed the clinical experience in the treatment of medulloblastoma with radiotherapy at Duke University Medical Center. One hundred and twenty-seven patients treated between January 1, 1940 and December 31, 1983 were evaluated. The irradiation technique was reviewed and all irradiation doses were recalculated as minimum tumor doses in Gray (Gy). The mean follow-up was 24.4 years and the median follow-up was 26.5 years. The energy of the treatment machine was known in 102 cases. Sixty patients were treated with orthovoltage equipment and 42 patients were treated with megavoltage equipment. As a gross assessment of the impact of the details of radiotherapy treatment upon outcome, patients were grouped into excellent, good, fair, and poor treatment groups. Patients undergoing cranio-spinal axis (CSA) irradiation and receiving greater than or equal to 52 Gy to the posterior fossa and greater than or equal to 30 Gy to the clinically uninvolved remainder of the CSA were classified as having "excellent" technique. Patients undergoing CSA irradiation and receiving 40 to 52 Gy to the posterior fossa and greater than or equal to 20 Gy to the remainder of the CSA were classified as "good." Patients receiving 20 to 40 Gy to the posterior fossa and greater than or equal to 10 Gy to the spinal axis with or without prophylactic cranial irradiation were designated "fair." Any patient not fulfilling the above minimum criteria was categorized as "poor." The actuarial 5-year survival for the entire population was 33%. The 10-year survival was 21%. In 93 patients for whom records were detailed enough to allow categorization of treatment technique, 5-year actuarial survivals were: Excellent 37% (n = 17), Good 55% (n = 13), Fair 35% (n = 23), Poor 20% (n = 40). A complete surgical resection was not correlated with improved disease-free survival (DFS) in the excellent and good groups, but was correlated with an improved DFS in the fair and poor groups. The posterior fossa accounted for 62% of the failures in the 55 patients completing irradiation where the initial site of failure was known. An examination of patterns of failure in the spinal canal failed to demonstrate a dose response relationship above 10 Gy for spinal canal prophylactic irradiation. No patient developed recurrence beyond their period of risk as defined by "Collins' Law."(ABSTRACT TRUNCATED AT 400 WORDS)