Objective: The aim of this study was to determine the incidence of microsatellite instability of colorectal carcinomas (CRC) according to gender, age, and TNM stage. Study was conducted during two years at the Clinical Hospital Centre Osijek (CHCO). Study design: Cross sectional study with the archive data. Participants and methods: Analysis included archive data taken from Clinical department of pathology at CHCO. Study included 244 respondents, all of whom underwent colectomy in 2017 and 2018. We analysed present histological samples dyed with both standard (haematoxylin eozin) and immunohistochemical (IHC) methods. We used IHC methods to determine MLH1 (MutL Protein Homolog 1), MHS2 (MutSProtein Homolog 2), MHS6 (Mut Protein homolog 6), and PMS2 (Postmeiotic Segregation Increased 2) proteins. Results: Out of the total number of 244 respondents, 155 (51%) were male and 119 (49%) were female. Median patient age was 68 years. Respondents’ data was analysed in view of microsatellite instability status, MSS (Microsatellite stabile carcinomas) and MSI (microsatellite unstable carcinomas). There were 219 respondents with MSS carcinoma (90%), and 25 respondents with MSI type carcinoma (10%). There were no significant differences between those two groups in tumor size (χ2 test, P=0.10), Astler – Coller classification (χ2 test, P=0.75), and TNM stage (χ2 test, P=0.92). Statistically significant difference was found in cancer stability (χ2 test, P < 0.001). MSI carcinomas were found in ascendant colon in 52% of respondents, whereas 65% of the respondents had MSS carcinoma localised in colorectal part. One negative protein was found in 12 respondents (48%), while two negative proteins, in various combinations, were found in 13 respondents (52%). Conclusion: We can conclude that 10% incidence of MSI carcinomas justifies IHC examining of DNA repair enzymes. Because of more frequent localisation of MSI CRC in the right colon with different reaction to therapy, a higher significance should be given to this type of tumour.