CHILDREN'S CANCER GROUP Protocol CCG-9882 was designed to determine the effectiveness of hyperfractionated radiation for the treatment of children and young adults with brain stem gliomas. The study opened for the accrual of patients on September 21, 1988, and was closed on June 30, 1991. The first 54 children in the study were treated with irradiation doses of 100 cGy given twice daily to a total dosage of 7200 cGy. The next 66 children were treated with a similar daily regimen to a total of 7800 cGy. Tumors were diagnosed by clinical and radiographic criteria. Decisions about the need for surgery were left to the discretion of the treating neurosurgeon; tissue diagnosis did not alter the therapy in patients with diffuse infiltrating tumors. We reviewed the neuroradiology and neurosurgery reports as well as the pathological specimens of children entered on the study. By magnetic resonance (MR) imaging criteria, tumors involved the majority of the brain stem in 76% of cases; only three patients had tumors localized to the midbrain or medulla. Operations were performed on 56 of 120 patients (47%). Cerebrospinal fluid shunts were inserted in 27 (23%) of the children; insertion of a shunt was the only operation in 11, and a shunt was inserted in conjunction with a tumor operation in 16. Tumor operations were performed in 45 (38%) of the patients; 24 had stereotactic biopsies, and 21 had craniotomies. Of the 21 patients who had craniotomies, only biopsies were performed in 11; partial tumor resections were performed in 5 patients and subtotal resections in 5. Postoperative neurological complications were reported in five children (11%); in two cases, the neurological complications occurred after stereotactic biopsies, and in three, these complications occurred after open biopsies. All biopsy specimens showed either low-grade or high-grade astrocytomas. It has been shown that magnetic resonance scans are highly specific for diagnosing brain stem gliomas and obviate the need for histological confirmation before radiotherapy in most patients. However, many patients with brain stem gliomas still undergo operations.