The tri-institutional Genetically Modified Animal (GMA) Phenotyping Service exists to serve investigators at Memorial Sloan Kettering Cancer Center, The Rockefeller University, and the Weill Medical College of Cornell University by providing an extensive baseline phenotypic profile of genetically modified animals. Such a comprehensive baseline characterization will be invaluable to investigators unfamiliar with normal anatomy, histology, physiology, and age- or strain-related background lesions. Furthermore, evaluating the entire animal, as opposed to a specific tissue or organ system, will help to identify unanticipated phenotypic changes.