Percutaneous nephrostomy was performed using 18 guage pucture needle under ultrasonic guidance in 58 patients, 98 cases with hydronephrosis (bilateral; 15 cases, repeat nephrostomy; 25 cases). The causes of the hydronephrosis were malignancy(33 patients, 65 cases), benign diseases(18 patients, 25 cases), and unknown causes(seven patients, eight cases). Successful nephrostomy was achieved in all cases. Major complication was not found, but seven(7.1%) minor complications, such as gross hematuria(four cases), perirenal urine leakage(two cases), and fever(one cases) were developed. The complication rate in our study was similar to that of other studies using 21 guage puncture needle. In conclusion, we think that the percutaneous nephrostomy using 18 guage puncture needle is a simple, safe, and cost and time effective procedure and it can replace the method using 21 guage puncture needle.