PURPOSE: To analyze asymptomatic adnexal masses at positron emission tomography (PET) with fluorodeoxyglucose (FDG) in correlation with histopathologic findings and evaluate FDG PET for assessing malignancy in comparison with transvaginal B-mode and Doppler ultrasonography (US) and magnetic resonance (MR) imaging. MATERIALS AND METHODS: Ninety-nine patients underwent static FDG PET of the abdomen. US scans were evaluated according to sonomorphologic scoring systems. Resistance index of tumor blood vessels was calculated. Transverse and sagittal T1-weighted MR images obtained before and after intravenous administration of gadopentetate dimeglumine with a fat-saturation technique and T2-weighted MR images were acquired at 1.5 T. Adnexal mass malignancy was first assessed with each modality and then with a combination of the three techniques. Final diagnosis was made with histopathologic evaluation. RESULTS: FDG PET depicted seven of 12 malignant and 66 of 87 benign asymptomatic adnexal tumors. False-negative PET results were obtained in five of seven stage pT1 a cystadenocarcinomas and tumors of low malignant potential but not in advanced-stage ovarian carcinomas. Small moderately intense FDG accumulations in the lower pelvis were caused by benign adnexal tumors or gastrointestinal activity in 21 of 27 cases. The overall sensitivities and specificities were 58% (95% Cl: 27.7, 84.8) and 76% (95% Cl: 65.5, 84.4), respectively, for FDG PET; 92% (95% Cl: 61.5, 99.8) and 60% (95% Cl: 48.7, 70.1), respectively, for US; 83% (95% Cl: 51.6, 97.7) and 84% (95% Cl: 74.5, 90.9), respectively, for MR imaging; and 92% (95% Cl: 61.5, 99.8) and 85% (95% Cl: 75.8, 91.8), respectively, for the combination of three modalities. CONCLUSION: Since the sensitivity of US is as high as that of PET, MR imaging, and the combination of three modalities, it remains the method of choice for diagnosis and assessment of asymptomatic adnexal masses.