Most colorectal cancers regardless of etiology are believed to arise from adenomatous polyps. Both environmental and genetic factors are important in colorectal carcinogenesis. Twenty five percent of patients with colorectal cancer have relevant family history. We tried to verify the spectrum of manifestations of hereditary non polyyposis colorectal cancer HNPCC and what practical preventive measures could be applied. In related families, 4 generations were studied via interviewing. Seventeen patients fulfilled the Amsterdam’s criteria for the diagnosis of HNPCC (Lynch II), with a mean age of 59.11 11.75, 10 patients were females and 7 were males. All were not smokers. The pedigree we mapped for these families showed an autosomal dominant inheritance. HNPCC is heterogeneous syndrome. Although has certain gene defect. We should always think of HNPCC in presence of positive family history of colorectal cancer or other malignancy specially those affecting young age groups. Regular colonoscopy and aspirin prophylaxis are important preventive measures.