Hereditary nonpolyposis colorectal cancer (HNPCC) is comprised of the following: the cancer family syndrome (CFS), or Lynch syndrome II, which shows early-onset proximal colonic cancer predominance and other associated extracolonic adenocarcinomas, particularly endometrial carcinoma; and hereditary site-specific colon cancer (HSSCC), or Lynch syndrome I, which shows all of the same characteristics, except for extracolonic cancer. Nine families with CFS and two with HSSCC provided the resource that was tested for biomarkers (see companion article). All families were meticulously evaluated for genealogy and cancer verification. Biologic specimens were obtained during field visits to areas of closest geographic proximity to the families. Cancer education and recommendations for surveillance/management were provided to patients and their physicians. Additionally, 40 families (about 3000 individuals) with either CFS or HSSCC have been ascertained. Syndrome cancers were restricted to direct-line relatives as opposed to nonbloodline relatives, arguing against involvement of environmental factors. One documented clinical feature was a predilection for proximal versus distal colonic cancer in both CFS and HSSCC kindreds. This has important clinical significance in that it clarifies the need for instituting effective surveillance earlier to detect the predominantly proximal colonic cancers.