Objectives: To study hepatitis B virus (HBV) markers (HBsAg, HBeAg and anti –HBC antibody) together with circulating immune complexes (CTC), C3 and liver function tests in children with renal diseases. Methods: Subjects studied were, 20 healthy children as a control group, 20 patients with acute glomerulonephritis. (AGN) and 50 patients with nephrotic syndrome (NS), 25 during relapse and 25 patients during remission. Results: The incidence of HBsAg and HBeAg was insignificantly different in patients with AGN and in nephrotic patients in comparison with the control group. However, the incidence of anti-HBC antibody was significantly higher in patients with AGN (30%) and in nephrotic patients during relapse (44%) compared to healthy children. There was a significant increase in serum creatinine, SGPT, SGOT, alkaline phosphatase, serum bilirubin and CIC with a significant decrease in serum albumin and C3 in AGN patients with positive anti-HBC antibodies in comparison to Anti-HBC negative patients. In nephrotic patients during relapse, the incidence of frequent relapse was significantly higher in anti-HBC antibody positive patients, and the serum SGPT, SGOT, alkaline phosphatase, bilirubin, CIC were significantly high and C3 was significantly low in comparison with Anti-HBC antibody negative patients. Renal biopsy was performed in 4 anti-HBC antibody positive nephrotic patients and showed membranoproliferative glomerulonephritis (2 cases), membranous glomerulonephritis (1 case) and focal glomerulosclerosis (1 case). Conclusions: From these results we suggest that infection with HBV may be one of the aetiological factors of AGN and NS in Egypt. Recognition of secondary glomerulonephritis has significant prognostic and therapeutic implications.