Sixty-four adult patients with malignant glioma entered into a Phase II study on the use of accelerated hyperfractionated radiation therapy. Histology included anaplastic astrocytoma (AA) in 15 patients and glioblastoma multiforme (GBM) in 49 patients. Treatment consisted of radiation therapy doses of 66 Gy in 44 fractions in 22 treatment days in 4.5 weeks, fractions of 1.5 Gy, b.i.d. 1,3-bis(2-chlorethyl)-1-nitrosourea (BCNU) 80 mg/m2 and hydroxyurea 800 mg/m2 were both given on treatment days 1, 6, 11, 16, and 21 during the irradiation course. Median survival time for all 64 patients is 61 weeks (range; 12-163 weeks) from the date of starting irradiation. Median time to tumor progression (MTP) for GBM patients is 31 weeks, and 1-year and 3-year progression-free survival (PFS) are 16% and 0%, respectively, while MTP for AA patients is not attained yet, and 1-year and 3-year PFS are 100% and 73%, respectively. On univariate analysis of prognostic factors for GBM patients, younger age, total or subtotal tumor removal, and frontal tumor location are associated with a better prognosis. A multivariate analysis confirmed the importance of the extent of surgery and tumor site and revealed the interfraction interval (4.5-5.0 hours vs 5.5-6.0 hours, p = .041) as an important prognostic factor. Acute and late toxicity is not increased. Longer follow-up and more patients are needed to evaluate tumor control and toxicity in AA patients.