The effects of radiation therapy on 29 brain stem gliomas in childhood were evaluated by computed tomography (CT). The patients received radiation of 2 Gy/day as a single fraction, 5 day a week with a total dose of 40 to 60 Gy. Initial CT findings of brain stem gliomas were divided into two types: diffuse and localized. Of 29 children, 5 had localized and 24 had diffuse tumor. Histological diagnoses were available for 18 patients, 4 with localized and 14 with diffuse tumor. All of the localized tumors were astrocytomas and diffuse tumors included 13 anaplastic gliomas (glioblastomas), 3 anaplastic astrocytomas, and one astrocytoma. Complete response or partial response to radiation therapy was observed on CT in 100% (5/5) of the localized tumors and 46% (11/13) of the diffuse tumors at the first evaluation. Contrary to expectation, low-grade gliomas responded much better to radiation therapy than high-grade gliomas. The response rates were 80% (4/5) in astrocytoma, 67% (2/3) in anaplastic astrocytoma, and 38% (5/13) in anaplastic glioma. In the follow-up CT after radiation therapy, a delayed effect was observed in only one of the 24 diffuse tumors. Nine of 10 children who had a re-irradiation following the recurrence experienced very little benefit. None of the patients with localized tumors have shown evidence of tumor progression or recurrence, and the quality of their life has been excellent. On the other hand, all of the patients with diffuse tumor died within 20 months after initial treatment. The results of this study suggest that radiation therapy is beneficial for localized tumors but not for diffuse tumors, and new treatments need to be developed for diffuse tumors.