The aim of our study was to investigate proliferation and apoptosis in ovarian stromal hyperplasia and hyperthecosis in reproductive women with and without polycystic ovarian disease. We have studied 104 patients with a histological diagnosis of ovarian stromal hyperthecosis and stromal hyperplasia. Paraffin sections were stained by hematoxylin-eosin, von Gieson and immunohistochemistry for Bcl-2 (anti-apoptotic protein) and Ki-67 antigen (proliferation marker). We assessed the number of Bcl-2-positive and Ki-67-positive cells. The patients were divided into 4 groups: group 1 -- 33 patients with polycystic ovarian disease and coexistent stromal hyperthecosis, group 2 -- 28 patients with polycystic ovarian disease and coexistent stromal hyperplasia, group 3 -- 24 patients with ovarian stromal hyperthecosis, group 4-19 patients with ovarian stromal hyperplasia. The results suggest that in ovarian stromal hyperthecosis coexistent with polycystic ovarian disease luteinized stromal cells show high proliferation activity and resistance to apoptosis, and internal and external theca cells show resistance to apoptosis. In ovarian stromal hyperplasia coexistent with polycystic ovarian disease, hyperplastic stromal cells show high proliferation activity and resistance to apoptosis. Proliferation activity is also increased in vascular endothelial and smooth muscle cells. Internal and external theca cells show resistance to apoptosis. In ovarian stromal hyperthecosis without polycystic ovarian disease, luteinized stromal cells show high proliferation activity and resistance to apoptosis. In ovarian stromal hyperplasia without polycystic ovarian disease, hyperplastic stromal cells show high proliferation activity and potential susceptibility to apoptosis. Proliferation activity is also increased in vascular endothelial and smooth muscle cells. These characteristics of proliferation and apoptosis have meaning in pathogenesis of ovarian stromal hyperthecosis and stromal hyperplasia with and without polycystic ovarian disease.