Between January 1, 1983 and December 31, 1992, 805 patients with asymptomatic proteinuria and/or hematuria were selected in the mass screening of 56,269 adults. We conducted prospective long-term follow-up studies of these patients and evaluated their clinical findings and renal histology. They were divided into three groups according to the first dipstick urinalysis findings: 478 patients with pure hematuria (H), 150 patients with concomitant hematuria and proteinuria (H & P), and 177 patients with proteinuria (P). The mean follow-up period was 5.80 +/- 4.42 years. Of the 478 patients with H, a specific cause of hematuria was found in 46 (9.6%), the remaining 432 (90.4%) patients were diagnosed as having asymptomatic hematuria (ASH). During the follow-up period, in the ASH patients, hematuria disappeared in 44.2%, 43.7% had persistent microhematuria without proteinuria, and 10.6% manifested proteinuria, none of the patients showed renal insufficiency. Of the 150 patients with H & P, 134 were diagnosed as having asymptomatic H & P. During the follow-up period, the hematuria and proteinuria disappeared in 16.4% of these patients, the proteinuria disappeared in 8.2%, and 14.9% of the patients showed renal insufficiency. Of the 177 patients with P, 151 were diagnosed has having asymptomatic P. During the follow-up period, proteinuria disappeared in 23.2%, and 10.6% showed renal insufficiency. Renal biopsy was performed in 151 patients in the study population who had a moderate degree of proteinuria; 68.2% of these patients had IgA nephropathy, 12.6% had non-IgA mesangial proliferative GN, 6.0% had membranous nephropathy, 5.3% had minimal change, and 2.6% had focal and segmental glomerular sclerosis. This study of the mass screening of urinalysis in asymptomatic adults showed that although the patients with pure hematuria did not exhibit renal insufficiency, 10.6% of these patients were proteinuric during the follow-up period. Therefore, careful observation and management are needed in these patients.