The authors performed percutaneous antegrade pyelography guided by ultrasound on 33 patients, from June 1982 to October 1984, at the department of radiology, Busan National University Hospital. The results obtained were as follows: 1. Of the 31 cases, 17 cases (51.5%) were female and 16 cases (48.5%)were male, and age distribution was nearly even, but most prevalent age goup was third decade. 2. Comparing intravenous pyelographic findings with ultrasonographic findings, pyelographically nonvisualized kidney 15 cases(45.5%) were hydronephrosis 12 cases, multiple cysts 2 cases, and intratrnal cystic mass 1 case, ultrasonographically. Pyelographically hydronephrosis 9 cases (27.3%) were all hydronephrosis, ultrasonographically. Intrarenal mass 5 cases (15.2%)were all intratrnal cystic mass, NVK with air in kidney 1 case (3.0%) was air in perirenal space, partial NVK 1 case (3.0%) was perirenal fluid, suprarenal mass 1 case(3.0%)was suprarenal intrarenal and huge perirenal cystic asses, ultrasonographically. 3. On technical reliability of antegrade pyelography under ultrasound guide, 31 cases(93.9%) could be done fluid aspiration and visualization, and 2 cases (6.1%) could be only done fluid aspiration butfailed visualization, 31 successful cases were visualization of collecting systems 23 cases, visualization of cyst 6 cases, and visualization of perirenal space 2 cases, 2 partial successful cases were perirenal injection 1 case and parenchymal injection 1 case. 4. On fluid aspiration, 22 cases (66.7%) were clear, but 11 cases(33.3%) were not clear, which were pus 7 cases, turbid urine 2 cases, bloody urine 1 case, and bloody pus and air 1 case. 5. Comparing ultrasonographic findings with antegrade pyelographic findings, ultrasonographically hydronephrosis 21 cases revealed obstruction in 16 cases, antegrade pyelographically, which were consisted of ureteral stricture 14 cases, ureteral stone 1 case, and ureteral mass 1 case, nonobstruction in 4 cases, which were consisted of pyonephrosis 2 cases, posterior urethral valve 1 case, and megaureter 1 case, and other 1 case was visualization failure. Ultrasonographically intrarenal cystic mass 6 cases were simple renal cyst 4 cases, and infected renal cyst 2 cases, antegrade pyelographically. Multiple cysts 2 cases were lobulated huge renal cyst 1 case, and visualization failure 1 case, which was multi-cystic kidney. Air in perirenal space 1 case was emphysematous pyelonephritis, suprarenal cystic mass 1 case was complete duplication with ectopic ureteral orifice, perirenal fluid 1 case dut to kidney fracture was perirenal fluid, and intrarenal and perirenal cystic mass was perirenal abscess, antegrade pyelographically. 6. On analysis of antegrade pyelography result as next diagnostic step of ultrasound, 31 successful cases were 27 conclusive diagnostic cases(87.1%), and 4 hephful diagnostic cases(12.9%) with percutaneous antegrade pyelography guided by ultrasound. 7. Antegrade pyelography pr vides significant diagnostic information on the nature of the obstructive lesion and can be performed as an adjunct to retrograde study or as an alterative to a pyelogram. 8. Ultrasonographic examination could be performed easily in diagnosis of renal and perirenal diseases as non-invasive method without risk of radiation hazard, and was not influenced by renal function. 9. Ultrasound is considered a most advantageous aid to the performance fo antegrade pyelography and has yielded valuable diagnostic information in patients with obstructive hydronephrosis.