Among patients with enchondromatosis, those with Ollier's disease are usually considered to be at a lower risk for extra-osseous malignancy than those with Maffucci's disease. However, several reports suggest that Ollier's disease may also be associated with gliomas. We report here the youngest patient in the literature (16 years) to be detected with a brain tumor and Ollier's disease. This is also the first case with diffuse brain stem involvement. Thus, counselling of patients with Ollier's disease may become more difficult than initially thought.