A deletion polymorphism in the angiotensin-converting enzyme (ACE) gene has been reported to be a risk factor for progression to chronic renal failure in immunoglobulin A nephropathy (IgAN). In this study, we investigated the association between ACE gene polymorphism and clinical findings, early biopsy findings such as the extent of mesangial proliferation, focal lesions (capsular adhesions, glomerulosclerosis, and crescents), and the glomerular area in childhood IgAN. Genomic DNA was obtained from 97 patients and control subjects. Gene polymorphisms, consisting of an insertion (I) or deletion (D) of the 287-base pair Alu sequence, were detected using the polymerase chain reaction. The extent of capsular adhesions and glomerulosclerosis was significantly higher in patients with the ID/DD genotypes than in those with the II genotype (ID/DD v II: 8.0%+/-1.4% v 2.5%+/-0.8% [P = 0.017] and 5.1%+/-1.3% v 1.4%+/-0.6% [P = 0.028], respectively). Whereas there was no difference in the extent of mesangial proliferation and crescents between the ID/DD genotypes and the II genotype. Urinary protein excretion at the time of biopsy was significantly greater in patients with the ID/DD genotypes than in those with the II genotype (1.02+/-0.15 g/d/m2 body surface area v 0.56+/-0.13 g/d/m2 body surface area; P = 0.012). These results indicate that ACE gene polymorphism may not influence the extent of mesangial proliferation and crescents that are acute lesions. However, the ID/DD genotypes are associated with chronic lesions, such as capsular adhesions or glomerulosclerosis and urinary protein excretion in childhood IgAN.