OBJECTIVES: The characteristics of synovitis in juvenile idiopathic arthritis (JIA) are important to evaluate, as they define several clinical categories. The metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints are frequently involved. Few studies have investigated peripheral joint evaluation using ultrasonography, a sensitive tool for detecting subclinical synovitis. Our objectives here were to compare clinical and ultrasound evaluations of MCP and MTP joint synovitis and to determine the prevalence of predefined ultrasound abnormalities in JIA patients and healthy controls. METHODS: Standardized physical and ultrasound assessments of the same joints were done in 31 consecutive patients with JIA and 41 healthy volunteers. Joint pain, motion limitation, and swelling were recorded. Ultrasonography was performed on the same joints by 2 trained sonographers who recorded synovial fluid, synovial hypertrophy, erosion, and power Doppler signal. Intraobserver reproducibility of ultrasonography was assessed. RESULTS: Of 558 peripheral joints examined in JIA patients, 69 (12.5%) had ultrasonographic synovitis and 83 (15%) had abnormal physical findings. All the physical abnormalities were significantly associated with ultrasonographic synovitis (P < 0.0001) but agreement was low between ultrasonographic and physical findings. Ultrasonographic synovitis was most common at the feet (59.4%), where it was detected clinically in only 25% of cases. Ultrasonographic synovitis was associated with the presence of synovial fluid. Cartilage vascularization was found in 2 (4.2%) healthy controls. CONCLUSION: Ultrasonography is useful for monitoring synovitis in JIA. Subclinical involvement of the MTP joints is common. Clinicians should be aware of the specific ultrasonographic findings in children.