Since 1998, mass urine screening tests have been performed on Korean school children. We have analyzed those patients who showed abnormal urinary findings in the school screening program. Between January 1998 and January 2000, 452 children with abnormal urinary findings visited the Pediatric Kidney Center, Kyung-Hee University Hospital. Sex, age, 24-h urine creatinine clearance, ultrasonography, Doppler scans and renal biopsies were reviewed retrospectively. Results of initial urinalysis are divided into three groups: solely hematuria group (228 cases, 50.4%), solely proteinuria group (98 cases, 21.7%), and combined hematuria and proteinuria group (79 cases, 17.5%). Among the biopsied cases, the proportions representing renal parenchymal diseases were as follows: IgA nephropathy 11.3%, mesangial proliferative glomerulonephritis 21.9%, others 3.8%. Among the three groups, the combined hematuria and proteinuria group had more frequent chronic renal disease (57.7%) than the other groups. Chronic renal disease was detected in 36.9% of all visiting subjects. In the school screening program a significant number of patients showed abnormal urinary findings, which were associated with chronic renal diseases especially in the combined hematuria and proteinuria group. In conclusion, mass urine screening tests should be mandatory to detect asymptomatic chronic renal disease in school children.