We present one adult patient with medulloblastoma who developed polysomnographically documented obstructive sleep apnea after posterior fossa surgery. The sleep apnea worsened in conjunction with clinical and imaging-conrmed neoplastic progression and clinically improved after craniospinal radiation therapy. Medulloblastoma or its surgical treatment has never before been implicated in a sleep-related breathing disorder. We discuss possible mechanisms for its occurrence and management implications. Neuro-Oncology 1, 289-291, 1999 (Posted to Neuro-Oncology [serial online], Doc. 99-08, September 9, 1999