AIM: To assess the expression of Ki67 as prognosticator in rectal/recto sigmoid cancer.METHODS: Samples from 146 patients with rectal and recto sigmoid cancer were studied for expression of Ki67 and its prognostic significance in comparison with clinicopathological predictors of survival. Formalin-fixed, paraffin-embedded tissues from 6 (4.1%) patients with T1, 26 (17.8%) with T2, 94 (64.4%) with T3, and 20 (13.7%) with T4 tumors were studied. Ki67 expression was determined immunohistochemically. Samples were divided according to mean value into high (＞40%) and low (≤40%) expression. Areas of extensive proliferation (＞50%) were defined as hot spot areas. RESULTS: Hot spot areas were present in samples regardless of histopathological grade. Lower TNM and Dukes stage and higher expression of Ki67 and presence of Ki67 hot spot areas in histopathological samples were associated with better survival, whereas no association was observed with histopathological grade (P = 0.78). In Cox multivariate regression analysis, significant prognostic factors were Dukes stage (P＜0.001), presence of lymph node metastases (P = 0.015), age (P = 0.035) andpresence of Ki67 hot spot areas (P = 0.044). CONCLUSION: Proliferative activity as measured by Ki67 in rectal cancer is associated with survival improvement compared with patients with low Ki67. Areas of prognostically significant increased proliferation were found independently of histopathological tumor grade.