From 1970 to 1997, 63 patients with medulloblastoma were treated with craniospinal irradiation followed by a posterior fossa boost. There were 38 males and 25 females with a median age of 9 years (range, 8 months to 53 years). Stage was T1-T3a in 50 (79%) and M0 in 38 patients (60%) according to the Chang staging system. Gross total resection of the primary tumor was achieved in 33 (52%) and median posterior fossa dose was 54 Gy, with 55 (87%) receiving > or =50 Gy. Median radiotherapy treatment duration was 49 days (range, 30-104 days) with 35 patients (56%) completing radiotherapy in <50 days. The most common reasons for a protracted radiotherapy treatment duration > or =50 days were hematologic toxicity (46%) and use of <1.6 Gy fraction size per day (29%). Chemotherapy was used in 22 (35%). Median follow-up time was 10.8 years (range, 2-28.5 years). The 5- and 10-year freedom from progression rates were 58% +/- 13% and 50% +/- 13%, respectively, whereas the 5- and 10-year posterior fossa control rates were 61% +/- 12% and 54% +/- 13%, respectively. On multivariate analysis, age > or =3 years, M0 status, > or =50 Gy PFB dose, radiotherapy treatment duration <50 days, and use of chemotherapy correlated with better freedom from progression and posterior fossa control rates. The 5- and 10-year freedom from progression rates were 67% +/- 15% and 64% +/- 16%, respectively, for patients with radiotherapy treatment duration <50 days and were 42% +/- 20% and 29% +/- 18%, respectively, for duration > or =50 days ( p= 0.0026, log-rank test). The 5- and 10-year posterior fossa control rates were 70% +/- 15% and 70% +/- 15%, respectively, for radiotherapy treatment duration <50 days and 46% +/- 20% and 33% +/- 19%, respectively, for duration > or =50 days ( p= 0.0037, log-rank test). In addition to age > or =3 years, M0 stage, use of adjuvant chemotherapy, and posterior fossa dose > or =50 Gy, our findings also reveal that radiotherapy treatment duration <50 days has a favorable prognostic outcome in patients with medulloblastoma.