Traumatic injury is the most common cause of acute joint pain and swelling in children. The most frequently involved joints in trauma are the knees, wrists, and elbows. Bilateral joint involvement suggests inflammatory arthritides, such as viral or juvenile rheumatoid arthritis. The knee and hip are the most commonly involved joints in pediatric septic arthritis. Fever or chills are usually present. The earliest x-ray finding in a septic hip is asymmetric joint-space widening from effusion. The most common organisms are S. aureus and H. influenzae. In sickle cell patients, Salmonella is an important consideration in all bone and joint infections. Early aspiration and intravenous antibiotics are essential to preserve joint function.