OBJECTIVE: Primary signet ring cell carcinoma of the colon and rectum is a rare form of adenocarcinoma of the large intestine. The purpose of this study was define the incidence, natural history and relation with hereditary nonpolyposis colorectal cancer (HNPCC). METHODS: We reviewed the medical records and pathology of 28 patients with primary signet ring cell carcinoma of the colon and rectum seen at the Instituto de Enfermedades Neoplasicas (INEN), between 1991 and 2002. RESULTS: In the present study the incidence was 5.09% of large bowel adenocarcinoma. Most patients present with late stage disease (Dukes stage C and D). In most cases the signet ring cells diffusely infiltrated through all layers of the intestinal wall (Borrmann IV). Male to female ratio was of 1 : 1.5, mean age was 55.5 and median age was 57 years (range 11 - 83 years). CONCLUSIONS: Comparison of our data with the literature showed some differences that could be related with biological characteristics of our people and different applied inclusion criteria. We couldn't define the relation between HNPCC and primary signet ring cell carcinoma of the colon and rectum.