Our aim is to analyze microsatellite instability (MSI) in polyps of the large intestine removed during endoscopic polypectomy. A total 97 patients (30 female and 67 male) were included into the study group. In those patients we performed polypectomy between 2004 and 2007 in the 2nd Department of Surgery, Jagiellonian University, Krakow. Thus allowed us to gather DNA from the polyp specimen and amplify it with polymerase chain reaction (PCR) with 5 primers for APC, p-53, BAX, BATR II and BAT-26 genes.In case of microsatellite instability in at least one of these 5 loci, another PCR products were tested using ABI PRISM 310 Genetic Analyser. In 97 patients we removed altogether 130 adenomatous polyps. The most frequent location for them was the sigmoid colon. Microsatellite instability was detected in 21 polyps (16,6%), loss of heterozygosity in 25 polyps (19%). In control colonoscopy performed 1 year later recurrence of polyps was detected in 15% patients (7% female, 15% male). Microsatellite instability in p53, DCC were the most frequent mutation loci. It is also characteristic that recurrence of polyps appears more often in patients with MSI.