A case of bilateral glenoid hypoplasia in a boy afflicted with posterior fossa medulloblastoma is described. Glenoid hypoplasia is a rarely reported bilateral finding either in subjects complaining of shoulder pain or abduction/adduction movements reduction as well as shoulder recurrent dislocations. In this patient as in most of those reported in the literature the finding was incidental and could have been easily overlooked. It consists of shallow, irregular glenoid fossae which are hypoplastic, whereas the humeral heads are normal in size and shape. At the present time there is no explanation for this anomaly.