PURPOSE: To evaluate ultrasonographic findings of neonatal patients who were confirmed and treated as hip joint septic arthritis and osteomyelitis. MATERIALS AND METHODS: We retrospectively examined clinical features & radiologic findings of 7 neonatal patients ranging from 8 to 28 days of age who were examined from January 1996 to December 1998 at nursery and were confirmed and treated on the diagnosis of septic arthritis and osteomyelitis. Clinical features of the patients were comparatively analyzed with radiologic findings including plain radiographs, ultrasonography, bone scan and MRI. We emphasized importance of ultrasonographic findings of these patients. RESULTS: Ultrasonography was performed first of all in all cases after the symptom onset. Other examinations were performed on the same day or a few days later after ultrasonography. Ultrasonography revealed abnormal finding in 85.7%(6/7) of all cases. Plain radiographs revealed abnormal finding in 28.6%(2/7). Bone scan revealed decreased uptake in 66.7%(2/3). MRI revealed abnormal signal intensity in 100%(3/3). Ultrasonographic findings of the patients were deep soft tissue swelling in 85.7%(6/7) of all cases, periosteal elevation in 57.1%(4/7), synovial thickening in 42.8%(3/7), synovial effusion in 42.8%(3/7), echogenic debris or clot in 28.5%(2/7), cortical erosion in 28.5%(2/7), and subperiosteal abscess in 14.2%(1/7). CONCLUSION: Ultrasonography is a useful modality to diagnose septic arthritis and osteomyelitis in neonatal hip.