[en] Purpose: To determine the prognostic significance of histologic grading in oligodendrogliomas. And to assess the role of postoperative radiotherapy in low-grade tumors and adjuvant chemotherapy in anaplastic tumors. Methods and Materials: The records of 38 consecutive patients with the diagnosis of oligodendroglioma were studied. Histologic grade was based on the Smith System and adjusted for the Kernohan's variables. Treatment of low-grade tumors consisted of surgery or surgery plus postoperative radiotherapy. High-grade tumors, anaplastic and malignant, had surgery and postoperative radiotherapy with or without adjuvant chemotherapy. Results: 23 patients with low-grade tumors showed improved 5-year progression-free survival compared to 15 patients with high-grade tumors (74% and 27% respectively), and improved overall 5-year survival (70% compared to 27%). Of the low-grade group, 16 patients receiving postoperative radiotherapy showed improved 5-year progression-free survival compared to 7 patients who did not receive adjuvant radiation (80% and 24% respectively). The overall 5-year survival was similar (86%). 10 patients of the high-grade group had anaplastic oligodendrogliomas. 5 patients receiving adjuvant chemotherapy showed improved 5-year progression-free survival compared to 5 patients not receiving adjuvant chemotherapy (60% and 20% respectively). The overall 5-year survival was similar (40%). The remaining 5 patients of the high-grade group had malignant oligodendrogliomas. These received adjuvant chemotherapy and had similar overall survival and progression-free survival, ie: 40% at 5 years. Conclusion: High-grade oligodendroglimas have worse prognosis than low-grade tumors, postoperative radiotherapy may offer some benefit prolonging time to progression of low-grade tumors. Similarly adjuvant chemotherapy may prolong time to progression of anaplastic oligodendrogliomas. Prospective randomized clinical trials are needed to more fully assess these issues