The favorable response of oligodendrogliomas correlates well with characteristic chromosomal losses, of which loss of the short arm of chromosome 1 is most predictive. Oligodendrogliomas are histopathologically heterogeneous tumors and, in addition to the classic honeycomb histology, fields of nonclassic histology are often encountered. Information about the distribution of 1p loss in various regions of oligodendroglioma is, therefore, important to interpret findings in tumor biopsies. In this study we investigated the distribution of 1p loss in multiple fields in 24 biopsy specimens of oligodendroglioma consisting of classic and nonclassic histology by fluorescent in situ hybridization and loss of heterozygosity analysis. By fluorescent in situ hybridization analysis, loss of 1p was found in all fields examined in 37% of the tumor samples, and no loss was detected in 46%. In fields of classic oligodendroglial and polar spongioblastoma-like histology, significantly more loss for 1p was found (p < 0.001 and p < 0.01, respectively). Although fluorescent in situ hybridization analysis indicated heterogeneity for 1p loss in the other 17% of tumors, loss of heterozygosity analysis of these samples pointed to homogeneity of 1p status in all fields. The 1p status of the fields with classic histology significantly correlated with the status of the other fields in the same tumors (Spearman's rho 0.918, p < 0.001). These results point to genotypic homogeneity for 1p in oligodendroglial tumors.