Gestational trophoblastic diseases (GTD) represent a group of malignancies classified as invasive mole, choriocarcinoma, and placental-site trophoblastic tumors. The overall cure rate in the treatment of this malignant disorder now exceeds 90%. The aim of this study is retrospectively to evaluate the clinical characteristics and effectiveness of single-agent chemotherapy (CT) and combination chemotherapy according to the World Health Organization (WHO) risk groups of gestational trophoblastic diseases. Thirty one patients with GTD were treated in our institute between 1990-1998. Median age at presentation was 29 years (range 19-70 years). All patients were classified with respect to the WHO scoring system. According to this system, patients were divided into three clinical groups: low-risk nonmetastatic (low-risk group with good prognosis), low-risk metastatic, and high-risk metastatic (high risk group with poor prognosis). Eighteen patients in the nonmetastatic low-risk group with favorable prognostic factors received single agent CT (methotrexate and folinic acid), while 3 patients with metastatic low-risk and 10 patients in the metastatic high-risk group with poor prognosis received combination CT (EMA-CO). Complete response (CR) was obtained in all patients in the low risk group with good prognosis, whereas 9/13 (69%) patients in the poor prognosis group achieved CR and 4 (31%) had partial responses. This clinical classification system may be currently prefer for determining initial therapy in women with malignant gestational trophoblastic tumors. And, our report confirms that the alternating EMA/CO regimen is a well-tolerated and effective combination for the treatment of women with high-risk GTD.