Kaposi's sarcoma (KS) is an angioproliferative condition that accounts for 6% of all malignancies in organ transplant patients. When we review the literature, the results of the studies comparing the different stages and the proliferative activity of the tumor are challenging. However, we found no previous study on Ki-67 protein expression in KS that correlates skin and organ lesions. In the current study, we investigated whether there is a correlation on the proliferative activity between skin and internal organ lesions in KS. Proliferative activity of 13 biopsy specimens of KS was assessed immunohistochemically using the monoclonal antibody MIB-1 (Ki-67). Mann-Whitney U test is used for statistical analysis and a P value < .05 was considered significant. Seven of 13 cases were skin and six were internal organ KS. For skin lesions, the mean MIB-1 proliferation index was 14.5%, and it was 13% for organ lesions. There was no significant association between skin and internal organ KS in regard to MIB-1 PI (P > .05). The findings suggested that the proliferative activity in KS does not differ in skin and organ lesions. On the other hand, it should be considered that the number of cases in our study was limited and further studies with a larger series are needed.