The objective is to study the role of power Doppler sonography (PDS) in assessment of therapeutic response in juvenile rheumatoid arthritis (JRA) of knee joint. Thirty patients (age range 3-11 years) of JRA with knee joint involvement were selected for this study. Clinical assessment and ultrasound was done on the same day and repeated at the end of second and sixth month of therapy. All patients received naproxen (15-20 mg/kg/day) for a period of 6 months. Total clinical score (TCS) was calculated as sum of scores of pain, articular swelling and functional impairment. PDS was performed and degree of vascularity was assessed and graded. Total USG score was obtained by adding sum of scores of synovial effusion, synovial thickening and PDS. Results were compared between the total clinical score and the total ultrasound score and between clinical groups at baseline, end of second month and end of sixth month. There were statistically significant differences between clinical and ultrasound indices and confirmed that PDS is more sensitive in detection and follow-up of clinically silent cases of JRA. PDS holds great promise for detection of active synovial inflammatory disease in sub-clinical cases of JRA and is useful in objective assessment of therapeutic response.