As research about array Comparative Genomic Hybridization (aCGH) unfolds, its applications are becoming an increasingly important part of the practice of medical genetics and laboratory clinical cytogenetics. Bassem Bejjani, at research professor at the Health Research & Education Center at Washington State University, examines the methodology of aCGH, recently developed platforms and numerous clinical applications of this innovative method of analysis. From the Series:Laboratory Medicine Grand Rounds