A case of dyschondroplasia associated with brain stem glioma: diagnosis by stereotactic biopsy. We present a 24-year-old patient with multiple chondromas of both hands, the pelvis, the left leg, and an associated brain stem glioma. There was no evidence of hemangioma or dyschromia, and the condition was diagnosed as Ollier's disease, a special type of dyschondroplasia like Maffucci's syndrome and Kast's disease. An increased overall risk for development of malignant skeletal and nonskeletal tumors is associated with Maffucci's syndrome. The risk of malignant degeneration is lower in Ollier's disease. A glioma in the pons and the right lobe of the cerebellum was found in this patient. The literature describes an association with gliomas in only 12 cases of dyschondroplasia and an infratentorial localization in just one case. Signs of malignancy were histologically confirmed in 7 cases without significant preponderance of any one type. Our patient had a low-grade brain stem astrocytoma with fibrillar and gemistocytic components. A stereotactic serial biopsy made it possible to rule out malignant degeneration. Stereotactic brain tumor biopsy as a routine neurosurgical procedure is particularly valuable for deep space-occupying processes and forms the basis for therapy. In the present case, irradiation was not recommended. 