Medulloblastoma is the most frequent malignant pediatric brain tumor. Considerable efforts are dedicated to identify markers that help to refine treatment strategies. The activation of the Wnt/beta-catenin pathway occurs in 10-15% of medulloblastomas and has been recently described as a marker for favorable patient outcome. We report a series of 72 pediatric medulloblastomas evaluated for beta-catenin immunostaining, CTNNB1 mutations, and studied by comparative genomic hybridization. Gene expression profiles were also available in a subset of 40 cases. Immunostaining of beta-catenin showed extensive nuclear staining (>50% of the tumor cells) in 6 cases and focal nuclear staining (<10% of cells) in 3 cases. The other cases exhibited either a signal strictly limited to the cytoplasm (58 cases) or were negative (5 cases). CTNNB1 mutations were detected in all beta-catenin extensively nucleopositive cases. The expression profiles of these cases documented a strong activation of the Wnt/beta-catenin pathway. Remarkably, 5 out of these 6 tumors showed a complete loss of chromosome 6. In contrast, cases with focal nuclear beta-catenin staining, as well as tumors with negative or cytoplasmic staining, never demonstrated CTNNB1 mutation, Wnt/beta-catenin pathway activation or chromosome 6 loss. Patients with extensive nuclear staining were significantly older at diagnosis and were in continuous complete remission after a mean follow-up of 75.7 months (range 27.5-121.2) from diagnosis. All three patients with a focal nuclear staining of beta-catenin died within 36 months from diagnosis. Altogether, these data confirm and extend previous observations that CTNNB1-mutated tumors represent a distinct molecular subgroup of medulloblastomas with favorable outcome, indicating that therapy de-escalation should be considered. Yet, international consensus on the definition criteria of this distinct medulloblastoma subgroup should be achieved.