Gestational trophoblastic disease represents a spectrum of lesions characterized by an abnormal proliferation of trophoblast, including partial mole, complete mole, invasive mole, choriocarcinoma, and placental site trophoblastic tumor, which have varying propensities for local uterine invasion and methastasis. Recent advances have demonstrated various clinicopathologic factors associated with gestational trohoblastic disease. But there are few reports on concerning factors related to persistence or malignant transformation in gestational trophoblastic disease. Increasing evidences have indicated that cyclin E is a nuclear protein essential for the G1-S phase transition and its overexpression has been reported to be correlated with certain cancers. To our knowledge, there has been no published study on the expression of cyclin E in gestational trophoblastic disease. The current study was conducted not only to examine the expression of cyclin E in a spectrum of gestational trophoblastic disease classified by the pathological diagnosis but also to determine whether there is any relationship between the cyclin E expression and clinical risk factors, such as patient's age, parity, initial serum beta-hCG, and its presistence. The immunohistochemical expression of cyclin E was determined in formalin-fixed paraffin-embedded sections of 3 hydropic abortions, 15 partial moles, 33 complete moles, 2 invasive moles and 3 choriocarcinomas. Cyclin E index was defined as the percentage of positively labeled nuclei per 1000 cells. Choriocarcinoma had a significantly higher cyclin E expression compared to hydropic chages(p=0.015); although there was a difference in cyclin E expression between complete mole and choriocarcinoma, this had no statistical significance(p=0.051). In contrast to our expectation, cyclin E expression was the lowest in invasive mole but numbers of cases were too small to draw any conclusion. comparison of cyclin E expression according to age, parity, initial serum beta-hCG, and persistence showed no significant difference. Our results suggest that expression of cyclin E may play an important role in malignant transformation of gestational trophoblastic disease. However, to examine the potential clinical value of cyclin E as a prognostic marker in gestational trophoblastic disease, prospective studies with a large number of cases are required.