Temozolomide is a novel second-generation oral alkylating agent with demonstrated efficacy and safety in patients with recurrent glioblastoma multiforme (GBM) and anaplastic astrocytoma (AA). A multicenter phase II trial was conducted to determine the efficacy and safety of temozolomide before radiotherapy in patients with newly diagnosed GBM and AA. Fifty-seven patients (51 adult, 6 pediatric) with newly diagnosed supratentorial GBM or AA were treated with temozolomide (200 mg/m ( 2 ) per day for 5 consecutive days every 28 days) for a maximum of 4 cycles. All patients were then treated with external beam radiotherapy. Twenty-two patients (39%) achieved objective response, including 6 (11%) with complete response (CR) and 16 (28%) with partial response (PR). Additionally, 18 (32%) patients had stable disease (SD). Of 21 patients (18 adult, 3 pediatric) with AA, 2 (10%) achieved CR, 5 (24%) achieved PR, and 8 (38%) had SD. Among adult patients with AA, the median progression-free and overall survival rates were 7.6 and 23.5 months, respectively. Among 36 patients (33 adult, 3 pediatric) with GBM, 4 (11%) had CR, 11 (31%) had PR, and 10 (28%) had SD. The median progression-free and overall survival rates among adult patients with GBM were 3.9 and 13.2 months, respectively. Temozolomide was safe and well tolerated in adult and pediatric patients. Grades 3 and 4 adverse events were reported in 16 (28%) and 7 (12%) patients, respectively. Temozolomide was safe and effective in treating newly diagnosed GBM and AA before radiotherapy. This pre-irradiation treatment approach appears promising, but will require additional evaluation in comparative studies.