Ultrasonographic findings of 12 cases of renal abscess were analized, and the results were as follows: 1) Theechogenicity of the renal abscess 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 lesions have changed hypoechoic mass on follow-upexamination. 3) Perinephric abscess was complicated in 6 cases(50%). 4) Ultrasound is noninvasive and accuratemethod for detection and follow-up study of renal and perirenal abscess.