Introduction. The most prevalent inflammatory bowel diseases (IBD) include ulcerative colitis (UC) and Crohn's disease (CD). Immune processes play a vital role in the etiopathogenesis of these conditions, involving both cellular and humoral response mechanisms. The aim of this study was to quantify CD40-and CD80-positive cells in the biopsy specimens of large intestinal mucosa from children with IBD. Materials and method. The study comprised 38 children aged between 3-17 years (mean 11.5±3.7 years) -20 boys (52.6%) and 18 girls (47.4%). Eighteen patients were diagnosed with UC on the basis of clinical manifestation, endoscopic and histopathological findings. Mean age of this subgroup was 11.55±4.07 years. A group of 10 children (mean age 12.30±2.83) diagnosed with CD was also included. The control group comprised 10 IBD-free children (mean age 10.28±4.07 years). The surface expressions of CD40 and CD80 were analyzed in large intestine mucosa biopsy specimens, fixed in formaldehyde, embedded in paraffin, and cut with a microtome into 4 µm slices. Results. The number of CD40-and CD80-positive cells in the large intestinal mucosa of children with Crohn's disease and ulcerative colitis was significantly higher than in the controls. The highest number of CD40+ and CD80+ cells was observed in the caecal mucosal membrane of Crohn's disease patients and in the rectal mucosa of individuals with ulcerative colitis. Conclusion. IBD is characterized by elevated, segment-specific, expression of CD40 and CD80.