Oligodendroglial tumors may rarely display striking desmoplasia resulting in unusual histologic patterns that have not been completely characterized. We reviewed the clinicopathologic findings of 7 such cases. Patients included 4 men and 3 women. Mean age at the time of primary surgery was 49 years (range, 31 to 57 y). All tumors were of World Health Organization grade III (4 anaplastic oligodendrogliomas and 3 anaplastic oligoastrocytomas). Characteristic morphologic features included tumor nests/nodules with surrounding fibrosis/desmoplasia (n=5), cords/single-cell infiltration (n=2), minigemistocytes (n=5), endothelial hypertrophy (n=6), and necrosis (n=1). Mean mitotic index was 9 mitoses per 10 high-power fields. Immunohistochemical studies demonstrated immunoreactivity for PDGFRα 1 to 3+ (5 of 6), PDGFRβ 3+ (n=3 of 3), and EGFR 1 to 2+ (n=5 of 6). p53 protein expression was 1-2+ and MIB-1 labeling index was moderate. Four tumors showed 1p19q codeletion, 1 tumor showed 1p deletion only, and 2 tumors showed intact 1p19q loci. t(1:19) was identified in 2 (of 3) tested cases, both also with 1p19q codeletion, and was absent in the case with 1p loss only. IDH1R132H mutant protein was detected in 3 (of 6) cases, and an IDH mutation (R132S) was identified in an additional case by pyrosequencing. Clinical follow-up was available in 6 (of 7) patients (mean follow-up of 64.2 mo). Five (of 6) developed recurrence/progression at a mean interval of 49.2 months after primary diagnosis. Only 1 patient died of disease, 22.5 months after primary diagnosis. Oligodendroglial tumors with prominent desmoplasia are rare. Most cases demonstrate 1p19q codeletion and IDH1 mutations, and behave as expected for anaplastic oligodendroglial tumors.