Fibroadenoma and phyllodes tumor are biphasic tumors ofboth stromal and epithelial elements. It was thought that biological behaviour ofthese tumors were determined by stromal elements. Cellular fibroadenomas behave as fibroadenoma so that their differentiation from the phyllodes tumor is important. The aim of the present study is to investigate the proliferative activity offibroadenoma, cellular fibroadenoma and benign phyllodes tumor. Five benign phyllodes tumor, 10 cellular fibroadenoma and 33 fibroadenoma were included in this investigation. Mitosis counting were performed on 10 consecutive high power fields in hematoxylen-eosin sections. Ki-67 scores were determined by counting the positive nuclear staining on 10 consecutive high power fields. According to median scores, both mitosis and Ki-67 scores were found to be statistically different in fibroadenoma group when compared to other two groups. Both scores of the cellular fibroadenoma group were lower than the phyllodes group but these differences were statistically insignificant. These results suggest that cellu1ar fibroadenoma are between fibroadenoma and benign phyllodes tumor according to their proliferative activity and these lesions may belong to a spectrum.