In colorectal cancer different levels of microsatellite instability (MSI) have been described. MSI-H (high) characterizes a unique clinical and pathological phenotype known as hereditary non-polyposis colorectal cancer syndrome, whereas MSI-L (low) and MSS (stable) are considered similar phenotypes without pathological implications. MSI has been also described as a frequent genetic alteration in a subset of gastric adenocarcinomas. However, the clinicopathological and prognosis significance of this abnormality in these tumors remains unclear. To investigate the role of genetic instability in gastric carcinogenesis we examined 10 microsatellite loci in 37 patients. MSI-H was found in 37.8% patients. We observed a trend of MSI-H tumors to be associated with elderly patients, intestinal histological type, advanced clinical stages and less aggressiveness with better survival. In conclusion, MSI-H can be considered as a good prognosis factor in a subset of gastric tumors.