Abscesses developing within the retroperitoneal spaces are complicated and serious infections. These abscesses present insidiously, leading to considerable mortality and morbidity. A high clinical suspicion can help diagnose and treat this potentially fatal illness. Computed axial tomography is the best diagnostic modality for retroperitoneal abscess. Computed tomographic scan is useful, not only for diagnosing the retroperitoneal abscess, but can be used for therapeutic drainage of abscesses in high-surgical-risk patients. We present an illustrative case of retroperitoneal abscess and discuss the pathogenesis of retroperitoneal abscess, diagnosis, and treatment.