Abscess of the iliopsoas muscle diagnosed by magnetic resonance imaging and ultrasonography. We have reported a case of abscess of the iliopsoas muscle, in which a limp and hip pain pointed toward pathology of the hip. The diagnosis in such cases may be difficult unless there is close attention to the clinical history and a good physical examination is obtained. One ultrasonographic examination of the hip in such a patient, subtle differences between the iliopsoas muscles should alert the radiologist to examine the psoas muscle. Ultrasonography is instrumental in demonstrating the solid or cystic nature of the iliopsoas mass, while MRI depicts the extent and proximity of adjacent organs. Once an iliopsoas abscess is diagnosed, treatment includes parenteral antibiotics and drainage. 