The iliacus muscle is closely associated with the psoas muscle, femoral nerve, hip joint, pelvic and intraabdominal structures; thus, its disorders may present as lower abdominal pain, hip pain, or femoral neuropathy. Iliacus pyomyositis, a primary bacterial infection of the skeletal muscle not secondary to a contiguous skin, bone, or soft-tissue infection, presenting as hip pain, femoral neuropathy, and sympathetic effusion of the hip joint in an 8-year-old boy mimicked septic arthritis of the hip joint. Computed tomography was helpful in delineating the accurate location of the lesion. Surgical drainage and appropriate antibiotic therapy led to complete resolution and full functional recovery.