In female patients, various nongynecologic pelvic masses may mimic gynecologic tumors and cause difficulty in diagnosis and treatment. Examples of these nongynecologic masses include various pelvic retroperitoneal tumors, bowel-related masses, and peritoneal lesions. These lesions may perplex gynecologic surgeons if they are not correctly diagnosed preoperatively. However, misdiagnosis can be avoided by careful observation of the mass per se and the pelvic anatomy related to the mass. A demonstration of both ovaries indicates that the mass is probably a nonovarian mass. Demonstration by Doppler US, CT, or MRI of the vessels supplying the mass may give a useful clue to the correct preoperative diagnosis. When prominent vessels are seen in the interface between the uterus and a juxtauterine mass, the mass is most likely a subserosal myoma. When these interface vessels are seen in the cranial aspect of the mass, it is probably not a gynecologic mass but rather a mass of bowel or mesenteric origin.