We combined two randomized prospective Brain Tumor Study Group data sets to analyze the effects of prognostic factors on survival by treatment group. Adjuvant chemotherapy increased long-term survival regardless of prognostic factors. Pathological review revealed that oligo dendrogliomas were overrepresented among long-term survivors independent of therapy. Prognostic factors do not predict benefit from adjuvant nitrosourea in malignant gliomas, and long-term survival with chemotherapy is not explained by oligodendroglial tumors.