PURPOSE: To investigate the role of gadolinium enhanced MR imaging in the evaluation of gestational trophoblastic tumors (invasive mole and choriocarcinoma). MATERIALS AND METHODS: Pre-enhanced T1-and T2-weighted images and gadolinium enhanced T1-weighted images of 34 gestational trophoblastic tumors (15 choriocarcinomas, 19 invasive moles) were evaluated retrospectively. Enhanced patterns of gestational trophoblastic tumors were analyzed. Morphologic differences and structural characterstics were analyzed by the evaluation of tumor margin, patterns of hemorrhagic necroses, development of intratumoral vascularity, and molar villi. Graded scores of MR findings between pre- and gadolinium enhanced images were given in the following criteria ; 1) visualization of tumor margin 2) distinction between tumor necrosis and zone of trophoblastic proliferation, and 3) molar villi. Statistical differences between graded scores of pre-and post-enhanced images were analyzed. RESULTS: Choriocarcinoma was a well-defined mass with peripheral rim enhancement and central hemorrhagic necrosis. Invasive mole was a ill-defined mass with partial necrosis, tiny cystic areas and increased intratumoral vascularity with dense reticular enhancement. Interface between tumor necrosis and zone of trophoblastic proliferation was better visualized on the gadolinium enhanced images than on the pre-enhanced images. Tumor margin and intratumoral molar villi were clearly discrimated on the gadolinium enhanced images only in invasive mole. There was no statistical difference in the visualization of tumor margin of choriocarcinoma between the pre-and post-enhanced images. CONCLUSION: Gadolinium enhanced MR image was helpful in the visualization of tumor characterstics in gestational trophoblastic tumors, and in the differential diagnosis between invasive mole and choriocarcinoma.