BACKGROUND: Data from the literature regarding the prognostic role of DNA mismatch repair system (MMR) in colorectal cancer are still controversial. AIM: The aim of the study was to identify the prognostic role of different phenotypic, clinical and pathological characteristics in microsatellite unstable vs. microsatellite stable colorectal cancer in terms of survival and disease free interval. METHODS: We conducted a retrospective study that included a total of 103 patients who underwent curative surgery for colorectal cancer. Immunohistochemistry testing revealed MLH1, MLH2, MLH6, PMS2 genes and mutations of the BRAF gene. We identified three groups of patients: patients with colorectal tumors with MSI produced by hypermethylation, (MLH1/BRAF+) group, patients with microsatellite instable tumours produced by genetic mutations MSI groupb(MLH1, MLH2, MLH6, PMS2) and patients with microsatellite stable tumours (MSS). RESULTS: The study shows that: MSI tumours (MLH1/BRAF+) group occur more frequently in women (p=0.05), on the right side of the colon (p=0.001). The 5-year survival rate was higher in patients with MSI tumours (MLH1/BRAF+) group than in those with microsatellite stable tumours, the differences were not statistically significant ; relapse rate was higher in patients with MSI tumors than in those with MSI tumours (MLH1/BRAF+) group (p=0.03) or with MSS tumors (p=0.004). CONCLUSIONS: The identification of microsatellite unstable colorectal tumours is an important molecular marker with role in recognition subgroups of patients with different phenotypic characteristics, survival and relapse rates.