The aim of the report was an attempt at assessing the role of vessels in morphological changes of the intestinal wall affected by ulcerative colitis and Leśniowski-Crohn's disease, as well as determining the character of vascular changes and comparing them in both the afore-mentioned diseases. The investigations included archival surgical materials originating from 42 patients with ulcerative colitis and 30 individuals with Leśniowski-Crohn's disease. A histological analysis was performed, along with an immunohistochemical assessment (reactions with antibodies against ICAM-1, VCAM-1, CD34, FVIII and UEA-1). The results were analyzed statistically. The investigations allowed for determining that vascular changes occurred in both diseases, being of a similar nature in ulcerative colitis and Leśniowski-Crohn's disease. The difference was chiefly quantitative. The detection of inflammatory in filtrates surrounding the vessels situated in otherwise unchanged or mildly changed intestinal segments proved the leading role played by vessels in both diseases. It should be stressed that perivascular inflammatory infiltrations involved all layers of the intestinal wall - not only in Leśniowski-Crohn's disease, but also in ulcerative colitis. The authors demonstrated a difference in expression intensity of various investigated vascular markers. In ulcerative colitis, higher values were obtained for the ICAM-1, CD34 and UEA-1 expression, while in Leśniowski-Crohn's disease, higher expression values were characteristic of VCAM-1 and FVIII. Numerous correlations were also detected in the expression of the investigated markers; the said correlations differed in both diseases. The results indicate that some histological differences (especially these involving the condition of vessels situated in the mucosa), as well as differences in the expression of immunohistochemical markers may be helpful in differentiating between the two diseases, and mostly in evaluating surgical materials.