AbstractHip ultrasound was performed on 44 children (114 exams) presenting with a painful hip or a limp thought to be due to hip disease. Effusions were found in 20 patients (21 hips). Hip ultrasound in combination with aspiration of the joint was found to be useful in diagnosis of osteomyelitis and septic joints, transient synovitis, trauma, and traumatic synovitis. We had no false positives or false negatives for hip effusions by ultrasound. In previous reports, absolute measurements have been relied upon for determination of hip effusions. We present a characteristic appearance of a capsule with and without abnormal joints fluid. The results of these 44 patients are summarized.