The chromosome (chr) 1p deletion is a favorable biomarker in oligodendroglial tumors and is even more powerful a marker when combined with chr 19q loss. As a result, the 1p deletion is taken into account more and more in clinical trials and the management of patients. However, the laboratory technique implemented for detection of this biomarker has been a topic of debate. To illustrate the usefulness of evaluating multiple loci, we here report two anaplastic oligodendrogliomas that were investigated using fluorescent in situ hybridization (FISH) and bacterial artificial chromosome (BAC)-array-based comparative genomic hybridization (aCGH). Indeed, segmental analysis using FISH, limited to chr 1p36 was unable to discriminate between complete and partial deletions of chrs 1p. However, complete and partial deletions of 1p are reported to have distinct clinical outcomes. Our results illustrate that aCGH (or other multiple loci technologies) provide complementary information to single locus technologies such as FISH because multiple loci technologies can evaluate the extent of the chr 1p deletion.