Eighty-one patients with pure supratentorial oligodendrogliomas underwent surgery alone (19 patients) or surgery plus postoperative radiation therapy (63 patients) between the years 1960 and 1982. The median survival time and the 5-, 10-, and 15-year survival rates for these 82 patients were 7.1 years, 54%, 34%, and 24%, respectively; these values were significantly different from those for an age- and sex-matched normal reference population. Univariate and multivariate survival analyses were performed on 13 possible prognostic factors including: patient age and sex; presence of seizures; site, size, side, computerized tomography (CT) enhancement, grade, and calcification of the tumor; and treatment (extent of surgical resection, lobectomy, radiation dose, and radiation field). Of these factors, tumor grade as classified by the Kernohan and St. Anne-Mayo methods was most strongly associated with survival. Patients with Grade 1 or 2 tumors by either grading method had a median survival time and 5- and 10-year survival rates of approximately 9.8 years. 75%, and 46%, respectively, compared to 3.9 years, 41%, and 20% for those with Grade 3 or 4 tumors. The extent of surgical resection was also associated with survival. The 19 patients who underwent gross total resection of their tumor had a median survival time and 5- and 10-year survival rates of 12.6 years, 74%, and 59%, compared to 4.9 years, 46%, and 23%, respectively, for the 63 who had subtotal resection. When comparing the 19 patients who underwent surgery alone with the 63 who had surgery plus postoperative radiation therapy, there did not appear to be a survival benefit to be gained from the addition of postoperative radiation therapy. However, the patients who had surgery alone tended to have gross total resections and lower tumor grades. Analysis of the subset of 63 patients who underwent subtotal resection alone or with radiation therapy showed that the median survival time and 5- and 10-year survival rates were: 2 years, 25%, and 25% for the eight patients with subtotal resection alone; 4.5 years, 39%, and 20% for the 26 patients with surgery and low-dose (less than 5000 cGy) radiation therapy; and 7.9 years, 62%, and 31% for the 29 patients receiving surgery and high-dose radiation therapy (greater than or equal to 5000 cGy), respectively.