Oligoastrocytomas are heterogeneous tumors that have molecular features that overlap with either oligodendrogliomas or astrocytomas. Differences in the frequency of chromosomal losses of 1p and 19q in oligodendrogliomas are related to tumor location, with a low rate of allelic loss in tumors of the temporal and a high rate in tumors of the frontal, parietal, and occipital lobes. To test the possibility of regional molecular heterogeneity in oligoastrocytoma, we examined a series of 203 gliomas including 68 oligoastrocytomas and two control groups of 73 oligodendrogliomas and 62 astrocytomas for allelic losses of chromosomal arms 1p and 19q, and TP53 mutations, and compared these data with tumor localization. Common molecular alterations were found in oligodendrogliomas and oligoastrocytomas arising in extratemporal sites. In respect to the molecular parameters analyzed, temporal oligoastrocytomas were either indistinguishable from astrocytoma or similar to temporal oligodendrogliomas. Oligodendroglial neoplasms can thus be separated into three molecular subsets, two of which include lesions with the morphological features of oligodendrogliomas and oligoastrocytomas and one resembling temporal oligoastrocytoma. Molecular subclassification thus unifies previous findings about prognosis, behavior, response to therapy, genotype, and location in oligodendroglial tumors.