Hereditary non-polyposis colorectal cancer (HNPCC) is the most common hereditary form of colorectal cancer (CRC), accounting for approximately 10% of the total CRC burden. HNPCC lacks premonitory physical stigmata, thereby making the family history crucial for diagnosis. Advances in molecular genetics during the past 2 years have led to the cloning of four HNPCC genes (MHS2, MLH1, PMS1 and PMS2). It is now possible to provide presymptomatic DNA testing followed by genetic counselling for gene carriers. Some studies have shown that adenomas in HNPCC are larger, more villous, and have more high grade dysplasia than sporadic cases, suggesting an accelerated adenoma-carcinoma sequence. Given the early age of onset and proximal predominance of CRC, we initiate colonoscopy at age 20-25 years and we recommend that it be performed every 1-2 years. The wealth of clinical and molecular genetic knowledge currently available to physicians about HNPCC can be used effectively for cancer control.