In a series of 18 individuals comprising parents of Angelman syndrome (AS) patients and AS patients with large deletions, microdeletions, and no deletions, we utilized fluorescence in situ hybridization (FISH) with genomic phage clones for loci D15S63 and GABRB3 for deletion detection of chromosome 15q11-q13. Utilization of probes at these loci allows detection of common large deletions and permits discrimination of less common small deletions. In all individuals the molecular cytogenetic data were concordant with the DNA deletion analyses. FISH provides an accurate method of deletion detection for chromosome 15q11-q13.