In a series of 125 patients examined ultrasonically for suspected abdominal aortic aneurysms, 15 patients (12%) had intraabdominal abnormalities unrelated to the aorta. In 12 of these patients, a retroperitoneal malignancy clinically mimicked an aneurysm. In the remaining three, other abnormalities were discovered in addition to an aneurysm.In one patient, a large uterine myoma was visualized; in another, large retroperitoneal lymph nodes subsequently proved to be lymphoma; in the third, enlarged lymph nodes in association with a carcinoma of the colon were discovered. Because of the high incidence of unsuspected findings, ultrasonography should become an essential part of the evaluation of this group of patients.