Hepatitis B virus (HBV)-associated glomerulonephritides have been increasingly reported, and the association between HBV and glomerulopathy is striking, especially in children. In this study, we investigated clinical and immunohistological features of HBV-associated glomerulonephritis in 14 children aged from 2.5 to 16 years (mean 10 years). The nephrotic syndrome was present in 9 (64%) and the nephritic syndrome in 8 children (57%). Five children had both nephrotic and nephritic syndrome together (35%). Renal insufficiency was determined in 4 of 14 patients (28%). Surface antigen (HBsAg) was present in all, with no history of clinically apparent hepatitis. Investigation of all renal tissue samples with light and immunofluorescence microscopy confirmed the diagnosis of membranous glomerulonephritis (MGN) in 6, membranoproliferative glomerulonephritis (MPGN) in 7, and IgA nephropathy (IgAN) in 1 child. Renal tissue samples were studied by the immunoperoxidase method for HBsAg in all cases; only in 4 children was HBsAg detected in the glomeruli. Examination of liver tissue samples was available in 4 cases, revealing chronic hepatitis in all, with additional development of cirrhosis in I and the presence of HBsAg in hepatocytes in all. Of the patients, 8 received corticosteroid treatment; I of them achieved a complete remission, while 4 had a partial remission with persistent proteinuria and hematuria. Four patients who received no treatment had a spontaneous remission within 5 months to 10 years following the onset of the renal disease. Two patients died of renal failure, while I died of intercurrent sepsis. The patient with IgAN received interferon-alpha2a and lamuvidine, which resulted in a remission and a marked decrease in HBV DNA titer. The remaining 2 were lost to follow-up. Although MGN has been reported as the nephropathy most commonly associated with HBsAg antigenemia in adults, our study revealed that MPGN could occur in children as well as MGN, without any clinical or historical evidence of hepatitis. The present study provides further evidence for a causal relationship between HBV hepatitis and HBs antigenemia-related glomerulonephritides in the pediatric age group. It also indicates the prognosis (71%) of the associated nephropathies with or without treatment is quite favorable in childhood.