Ultrasonographic findings of 12 cases of renal abscess were analized, and the results were as follows : 1) The echogenicity of the renal absecss was hyperechoic in 4 cases, isoechoic in 3 cases and hypoechoic in 5 cases. 2) Two out of 4 hyperechoic lesions and 1 out of 2 isoechoic lesionis have changed hypoechoic mass on follow-up examination. 3) perinephric abscess was complicated in 6 cases(50%). 4) Ultrasound is noninvasive and accurated method for detection and follow-up study of renal and perirenal abscess.