INTRODUCTION: The expression of the human Ki-67 protein is strictly associated with cell proliferation. The cell proliferation and kinetics of normal gastrointestinal tract are well known but the cell kinetics of adenoma in gastrointestinal tract is poorly understood. The aim of this study was to provide an immunohistochemical evaluation of the expression of Ki-67 antigen in different colorectal adenomas. MATERIAL AND METHODS: In the prospective study, we analyzed 65 colorectal adenomas. RESULTS: Proliferation indexes were found to steadily increase from normal mucosa to adenoma (p < 0.05). There was also a difference in the expression of Ki-67 between adenomas smaller and larger than 10 mm (p < 0.05). The expression of Ki-67 was strongly more often in villous adenomas as opposed to the tubular adenomas (p < 0.05). Reaction for Ki-67 were strong in adenomas with high grade atypia compared to low grade adenomas (p < 0.001). CONCLUSION: The expression of Ki-67 clearly shows differences between advanced and nonadvanced adenomas. The strong reactions of Ki-67 in adenomas with severe dysplasia show a close association with colorectal carcinoma. The immunohistochemical analysis (Ki-67) may be included as a part of routine pathological evaluation with conventional prognostic factors.