The diagnostic imaging characteristics of uterine carcinosarcoma have not been established because the tumor is very rare. We studied magnetic resonance (MR) imaging, power Doppler ultrasonography, and positron emission tomography (PET) in one such carcinosarcoma to define its imaging characteristics. On T1-weighted MR images, the tumor mass in the uterus was low-signal intensity and had a slight inhomogeneous appearance. On T2-weighted images, it had a heterogeneous appearance and was of medium- or high-signal intensity; marked flow void was apparent from the myometrium to the tumor mass. The MR flow void was also detected by power Doppler ultrasonography. Increased glucose metabolism was detected on PET images, suggesting a malignant tumor in the endometrial cavity. Combined diagnostic images with MR, power Doppler ultrasonography, and PET is recommended as the diagnostic method for uterine carcinosarcoma.