The authors reviewed the anatomy of the iliopsoas compartment and a spectrum of unusual lesions affecting structures in this compartment, with emphasis on the role of computed tomography (CT). Lesions in the iliopsoas compartment are caused by acute infection, tumor, or hemorrhage. The knowledge of detailed clinical data can help improve the diagnostic accuracy, particularly with regard to primary iliopsoas lesions. CT is useful for delineating the source of secondary iliopsoas lesions, guiding biopsy, and performing follow-up of treated lesions. Nonenhanced CT can help detect fresh hemorrhage, fat-containing tumor, and calcification, whereas contrast material enhanced CT optimizes imaging of infection, tumor, and aneurysm.