The study was carried out to analyze the roentgenological findings associated with clinical symptoms and physical findings about 18 cases of congenital hydronephrosis confirmed at the Dept. of Urology, Chonnam National University Hospital from Jan. 1977 to Dec. 1981. The results were summarized as follows: 1. The congenital hydronephrosis developed mostly in male (89%) and the distribution of age was between 4 months and 34 years. 2. The incidence of pathologial side was 10 patients in left, 3 patients in right and 5 patients in bilateral. 3. The most common etiological factor was congenial UPJ stricture (33%), others composed of aberrant. renal vessel (22%), ureterocele (22%), posterior urethral valve (11%), fibrous band (6%) and renal fusion (6%). 4. The main symptom was flank pain (56%) and in 7 cases (39%) abdominal mass was palpable. 5. On laboratory examination, serum BUN and creatinine level were normal in 14 cases (78%) and 15 cases (82%) respectively. In 2 cases of posterior urethral valves, renal function was severely damaged. 6. Intravenous pyelography was performed in all cases and showed pelvicaliceal dilatation in 13 cases, non-visualizing kidney in 5 cases, and characteristic crescent sign in one case.