Background/Aim. The aim of this study was to apply computer- assisted methodology in assessment of Ki-67 positivity in "adenoma-like" dysplasia associated lesions or masses (DALMs), and carcinoma in ulcerative colitis (UC), and to determine a new approach to grading of Ki-67 staining intensity. Methods. Immunohistochemical slides were quantitatively analyzed for estimation of proportion and intensity of Ki-67 positive-stained cells in a total of 50 "adenoma-like" DALMs (27 with low-grade dysplasia and 23 with high-grade dysplasia), and 17 adenocarcinomas associated with UC. The four grades of immunohistochemical staining intensity were established by an automated classification of nuclear optical densities. Results. The Ki-67 labeling index (LI) in low-grade dysplasia was significantly lower than in high-grade dysplasia, and carcinoma (p < 0.001). The Ki-67 LI of carcinomas was not significantly different from the value obtained in highgrade dysplasia (p > 0.05), however having the difference in percentage values of the moderate stained nuclei (p < 0.05). The overall average values of chromogene nuclear optical density, showed statistically significant differences between DALMs and carcinoma (p < 0.05), although not between normal mucosa and low-grade dysplasia (p > 0.05). Conclusion. The obtained results imply, according to the overall percentage of labeled nuclei, that high-grade dysplasia is very close to carcinoma, while there is the difference in the percentage of moderately stained nuclei. We showed that Ki-67 positivity have a different internal distribution which could be useful in analysing these lesions. These findings also, indicate the important biological differences between low-grade dysplasia and carcinoma in UC, and a low proliferative potential of the former. Automated image analysis permits an objective estimation of Ki-67 immunohistochemical staining in UCassociated dysplasia and carcinoma.