Carcinogenesis is a multistep process that begins with cancellation of normal controls on cell proliferation. Colorectal adenocarcinoma is a good example of carcinogenesis. The aim of this study was to evaluate the pro/iterative activity by Proliferating Cell Nuclear Antigen and Ki-67 immunohistochemistry in normal colon mucosa, colorectal adenoma and adenocarcinoma. Colorectal adenocarcinoma constitutes a heterogeneous group in prognosis. Relationship between proliferation index and conventional prognostic parameters (grade, staged venous and perineural invasion, lymph node metastasis, tumour growth pattern and lymphocyte response around the tumour) were also evaluated. Proliferation indexes were found to steadily increase from normal mucosa to adenoma and were highest in adenocarcinoma (P<0.05). There was also a difference in the Proliferating Cell Nuclear Antigen index between adenomas smaller and larger than 1 cm (P<0.05). No conventional prognostic factor was found to be related to the proliferative activity of the tumour. Our findings support the role of growth control in colorectal carcinogenesis. In the literature, results of studies reporting relationship between proliferation indexes and conventional prognostic factors are controversial. In this study we could not find any relation between them but it will be important to determine whether Proliferating Cell Nuclear Antigen and Ki-67 labelling indexes are significant predictors of prognosis and survival in colorectal adenocarcinoma