J.R.A is the most common rheumatic disorder of childhood .The knee is the most frequently affected joint. We speculated that U/S and MRI might be helpful as a diagnostic tool beside clinical assessment in evaluation of joint affection.The study included 40 JRA patients (20 patients with JRA in activity and 20 patients with JRA not in activity). Statistically significant difference was detected between the data detected clinically and that detected by U/S and MRI .And also between the results of U/S and MRI. So we conclude that the clinical assessment is of low reliability in evaluation of joint affection. However U/S is a simple, rapid, noninvasive and bedside tool but MRI examination especially following gadolinium injection is proved to be superior in evaluation of joint affection.