Clinicohistopathologically, we observed 109 patients with asymptomatic urinary abnormalities found via the Japanese school medical screening process. Follow-up was for a mean period of 9.3 ± 4.0 years. More than 80% of the patients had either IgA nephropathy (IgAN, 47 cases, 43.1%), thin membrane disease (TMD; 21 cases, 19.3%) or normal glomerulus (NG; 20 cases, 18.3%). Complete remission appeared in 60.0% of the NG cases, 14.3% of the TMD cases and in 19.1% of the IgAN cases, and remission was significantly high in the NG group (p < 0.01). No patient with TMD and NG ever progressed to the extent of pronounced proteinuria or renal failure. One patient deteriorated and required hemodialysis, and 2 patients developed renal insufficiency in IgAN. All of these cases possessed severe glomerular sclerotic change when the initial biopsies were performed. All IgAN cases that went into remission, however, had minor glomerular abnormalities. A positive family history of urinary abnormality was observed in 14.1% of both the IgAN group and the NG group, whereas we observed 71.4% in the TMD group, which was significantly high (p < 0.01). Other cases included 4 each with non-IgA proliferative glomerulonephritis, focal segmental glomerular sclerosis, membranoproliferative glomerulonephritis and Alport’s nephritis. It was concluded that the majority of patients (80.7%) with urinary abnormalities found via the school screening program had IgAN, NG or TMD. 74.5% of the IgAN group and 85.7% of the TMD group had long histories of urinary abnormalities extending into adulthood with no deterioration of the renal functi