The natural history and biological behavior of cystic glandular hyperplasia (CGH), which has been considered to be a precursor of endometrial carcinoma, still remain unclear. The present prospective study included 52 patients with CGH, who were followed up for 6 months to 5 years with occasional curettage, surgical procedures or hormonal therapy. The lesion disappeared in 35 cases (67.3%), persisted in 12 cases (23.1%) and became more serious in 5 cases (9.6%). Of these 5 cases, one case was found to have endometrial carcinoma during her follow-up. Nuclear DNA analysis was performed by Flow cytometry in 8 CGH cases. Eighty four point nine % of the cells from these 8 cases were in G0+1 phase, 8.3% in S phase and 7.4% in G2 + M phase. The proliferation index for CGH was 15.7%. Proliferative and mitotic activities of CGH were found to be similar to those of adenomatous hyperplasia, and the levels of these activities were between those of normal endometrium and atypical hyperplasia.G1.