OUTLINE: Patients are stratified according to disease characteristics (newly diagnosed anaplastic oligodendroglioma versus recurrent anaplastic oligodendroglioma). Patients receive oral temozolomide once daily on days 1-5. Treatment repeats every 28 days. Patients with progressive or recurrent disease (at baseline) continue treatment in the absence of disease progression or unacceptable toxicity. Patients with newly diagnosed disease continue treatment for a maximum of 4 courses before radiotherapy in the absence of disease progression or unacceptable toxicity. Patients with responding disease may receive an additional 6 courses after completion of radiotherapy. (Radiotherapy is not part of study treatment.) Patients are followed every 8 weeks for 2 years.