Transvaginal ultrasound is the method of first choice in patients with a suspected ovarian tumor. Computed tomography (CT) and magnetic resonance (MR) imaging are supplementary imaging procedures for the diagnostic evaluation of ovarian tumors. The major indications for a CT or MR examination are unclear ultrasound findings, the differential diagnosis of lesions and tumor staging. Dermoid cysts can be reliably diagnosed by both CT and MR imaging. The latter is superior in the demonstration of hemorrhagic lesions and in the evaluation of endometrial cysts. CT and MR imaging use identical morphological criteria for the differentiation of benign and malignant ovarian tumors; MR imaging is not superior to CT. For the staging of ovarian carcinomas, CT is the preferred imaging procedure. Contrast-enhanced MR imaging might be better for the evaluation of peritoneal carcinosis than other modalities.