OBJECTIVES: The aim of this prospective multicenter study was to evaluate and compare the diagnostic performance of PET/CT, MRI and transvaginal two-dimensional ultrasound (2DUS) in the preoperative assessment of endometrial cancer (EC). METHODS: 318 consecutive women with EC were included when referred to three Danish tertiary gynecological centers for surgical treatment. Preoperatively they were PET/CT-, MRI-, and 2DUS scanned. The imaging results were compared to the final pathological findings. This study was approved by the National Committee on Health Research Ethics. RESULTS: For predicting myometrial invasion, we found sensitivity, specificity, PPV, NPV, and accuracy for PET/CT to be 93%, 49%, 41%, 95% and 61%, for MRI to be 87%, 57%, 44%, 92%, and 66% and for 2DUS to be 71%, 72%, 51%, 86% and 72%. For predicting cervical invasion, the values were 43%, 94%, 69%, 85% and 83%, respectively, for PET/CT, 33%, 95%, 60%, 85%, and 82%, respectively, for MRI, and 29%, 92%, 48%, 82% and 78% for 2DUS. Finally, for lymph node metastases, the values were 74%, 93%, 59%, 96%, and 91% for PET/CT and 59%, 93%, 40%, 97% and 90% for MRI. When comparing the diagnostic performance we found PET/CT, MRI and 2DUS to be comparable in predicting myometrial invasion. For cervical invasion and lymph node metastases, however, PET/CT was the best. CONCLUSIONS: None of the modalities can yet replace surgical staging. However, they all contributed to important knowledge and were, furthermore, able to upstage low-risk patients who would not have been recommended lymph node resection based on histology and grade alone.