Purpose: To report the clinical course of adolescents with medulloblastoma, with specific emphasis on prognosis and pattern of relapse. Methods and Materials: We retrospectively studied the clinical course and outcomes of children aged 10–20 years with medulloblastoma, treated at centers throughout Canada between 1986 and 2003. To better assess time to relapse, a cohort of patients aged 3–20 years at diagnosis was generated. Results: A total of 72 adolescents were analyzed. Five-year overall survival and event-free survival rates were 78.3% ± 5.4% and 68.0% ± 6.2%, respectively. Late relapses occurred at a median of 3.0 years (range, 0.3–6.8 years). In univariate analysis, conventional risk stratification and the addition of chemotherapy to craniospinal radiation did not have prognostic significance. Female patients had improved overall survival (p = 0.007). Time to relapse increased with age in a linear fashion. After relapse, patients faired poorly regardless of treatment modality. Patients who did not receive chemotherapy initially had improved progression-free survival at relapse (p = 0.05). Conclusions: Our study suggests that adolescents with medulloblastoma might have a unique prognosis and pattern of relapse, dissimilar to those in younger children. They might benefit from different risk stratifications and prolonged follow-up. These issues should be addressed in future prospective trials.