Genetic diagnosis of Lynch syndrome II in an extended colorectal cancer-prone family. Knowledge of colon cancer genetics, with particular attention to precision in hereditary cancer syndrome diagnosis, can often enable highly targeted surveillance and management strategies for patients at high genetic risk. Unfortunately, the patient's family history of cancer is often given minimal attention, and knowledge of hereditary cancer syndromes is frequently limited. Indeed, many physicians still consider familial adenomatous polyposis (FAP) as the only genetic risk factor for colorectal cancer. This concern with FAP was noted in a colorectal cancer-prone kindred which for decades had been thought to manifest that syndrome. However, after meticulous genetic, medical, and pathologic studies, the cardinal phenotypic characteristics of Lynch syndrome II were observed. The potential for cancer control in current and future generations of families like this one clearly mandates the need for computerized registries which could transmit current information about hereditary colon cancer syndrome diagnosis, surveillance, and management. 