Research on the genetic, molecular genetic, clinical features, and natural history of HNPCC has shown tremendous progress and evolution during the past 25 years. Specifically, HNPCC's autosomal dominant mode of genetic transmission has now been documented through linkage studies of the gene at 2p (MSH2) and at 3p (MLH1) with the cloning of these genes. Also, the tumor spectrum has increased, which now, in addition to carcinoma of the colon, endometrium, stomach, and ovary, includes transitional cell carcinoma of the ureter and renal pelvis, and adenocarcinomas of the small bowel and pancreas. Surveillance and management protocols for patients at high risk should include full colonoscopy since 70% of the colon cancers occur in the proximal colon. Because of the marked excess of synchronous and metachronous colorectal cancers (CRC), no less than a subtotal colectomy should be performed at the time of initial CRC. Women, in addition to colonoscopy, require endometrial aspiration biopsy. Should they develop CRC and if their procreation is completed, we recommend that they consider prophylactic hysterectomy and bilateral salpingo oophorectomy at the time of their subtotal colectomy. Now that the deleterious genes at 2p and 3p have been identified, we are offering candidates, in whom the MSH2 or MLH1 mutation has been verified, an option of prophylactic subtotal colectomy as opposed to annual life time colonoscopy. With the development of the International Hereditary Nonpolyposis Colorectal Cancer Collaborative Group, knowledge can be disseminated worldwide about the public health importance of HNPCC and the need to implement highly targeted surveillance and management strategies in all clinical practice settings.