Microsatellite instability (MIN) has been found both in advanced and early gastric cancer. To find out the step played by MSI in gastric carcinogenesis, links between RER+ phenotype and clinical and pathological aspects have been studied. In this work our purpose is to analyze the relationship between MIN+ advanced gastric cancer and prognosis at 5 years after radical surgery. We investigated 34 patients affected by gastric cancer who underwent R0 surgical resection from February 1991 to October 1994. After that, they underwent a four-monthly follow-up for a minimum of 5 years. Genetic abnormalities have been searched including (a) those occurring in common-type CIN carcinomas and (b) those characteristic of MIN cancers. DNA extraction showed the presence of microsatellite instability (MIN) in 9 (26%) of the samples (vs. 74% of chromosomal instability CIN); none of them was M+ (vs. 12% of CIN cancers). Recurrence occurred in 2 out of 9 of the MIN cancers (22%) and in 21 out of 25 CIN cancers (84%). In conclusion, our data suggest that advanced gastric cancers with mutator phenotype show a better outcome at 5 years than the CIN phenotype.