Between 1988 and 1997, 28 children have had iodine-125 implants for CNS tumors performed in our institution. Ten had stereotactic implantation in the brain stem region, and nine had the diagnosis of brain stem glioma (8 diffuse pontine, 1 midbrain tumor). Their ages ranged from 1.8 to 12 years. All patients had histological confirmation of malignancy (7 high-grade glioma, 2 low-grade glioma, 1 PNET). Diffuse pontine glioma patients received external beam radiation (50 Gy) followed by a fractionated stereotactic boost of 3 Gyx4 fractions. After 4-6 weeks, patients were reevaluated for stereotactic interstitial I-125 therapy. The planned implant dose was 82.9 Gy to the enhancing tumor (4 cGy per h). Preliminary results indicated that no surgical complications were associated with the catheter placement. Four patients have died (7-9 months from diagnosis) and four patients remain alive (5-38 months from diagnosis, median 10 months). Two autopsies confirmed the presence of progressive glioblastoma multiforme and intralesional necrosis. In one patient who received an implant alone for midbrain LGA, necrosis without tumor was found on biopsy after 36 months. He was successfully treated with hyperbaric oxygen therapy. The implementation of permanent I-125 implants appears to have a role in the management of pediatric CNS malignancy. This study confirms the results of previous reports regarding the safety of stereotactic interstitial brachytherapy in the brain stem. Tumor control for patients with high-grade brain stem glioma remains poor even with high focal radiation doses.