Gliosarcomas are morphologically biphasic tumors composed of glial and sarcomatous elements. Only rare examples of gliosarcoma with oligodendroglial components have been reported. Seven patients with oligodendroglial tumors and a sarcomatous component were identified. Fluorescence in situ hybridization for 1p/19q was sought in glial and sarcomatous regions in all cases. Their mean age at diagnosis of gliosarcoma was 48 years (range 36 to 68) (F:M ratio=5:2). At first resection, the tumors included grade II oligodendroglioma (n=3), grade III oligodendroglioma (n=1), grade II oligoastrocytoma (n=1), and grade III oligoastrocytoma (n=2). The sarcomatous component developed in recurrent/progressive tumors in 6 cases but was a focal finding at first tumor resection in 1 and included fibrosarcoma (n=5), leiomyosarcoma (n=1), or pleomorphic myogenic sarcoma (n=1). Rhabdoid change was a focal finding in the sarcomatous component of 1 tumor. The glial component expressed both glial fibrillary acidic protein and S-100 in all cases, whereas the sarcomatous component at least focally showed smooth muscle actin (n=6), CD34 (n=4), S-100 protein (n=3), and epithelial membrane antigen (n=2) reactivity. Fluorescence in situ hybridization studies demonstrated 1p/19q codeletion in 5 cases, showed no evidence of deletion in 1 case, and technically failed in 1 case. Three of the 5 cases demonstrated 1p/19q codeletion in the sarcomatous component as well. Gliosarcomas with oligodendroglial elements are rare. The relatively frequent presence of 1p/19q codeletion in both glial and sarcomatous components supports the notion that the sarcomatous component represents a metaplastic change occurring in the glial element, the same mechanism active in classic astrocytic gliosarcomas.