Background: Hereditary nonpolyposis colorectal cancer (HNPCC) accounts for 3 to 5% of all colorectal cancer (CC). It is am autosomal dominant syndrome with 80% of penetrance for this disease. Aim: To analyse the pedigree and surgical treatment of HNPCC. Patients and methods: We retrospectively analyzed our database of CC selecting patients with HNPCC according to clinical criteria (Amsterdam II). We characterized our patient's pedigrees with telephonic interviews. Results: From 1111 patients operated on with CC we identified 13 (1.17%) with HNPCC. The mean age at diagnosis was 41.6 years (range: 23-75). Sixty two percent presented in International Union Against Cancer (UICC) stages I or II and none in stage IV. Seventy one percent of tumors were proximal to splenic flexure. In 5 patients the diagnosis of HNPCC was made postoperatively, after diagnosis of CC in their relatives. In all but one of the 8 patients with preoperative diagnosis of HNPCC, we performed a total colectomy. From the remaining 6 patients with partial colectomy, 2 developed metachronic CC. Two patients died of cancer and 4 other tumors. Twenty eight relatives were eligible for colonoscopic screening, but only 21 of them have been screened appropriately. Conclusions: Preoperative diagnosis should change the surgical treatment of HNPCC, preventing metachronic disease. Primary colonscopic screening allowed recommended frequency for colonoscopy.