Genetic hemochromatosis (GH) is associated with excess iron deposition in hepatocytes, which results in progressive hepatic injury. The pathogenesis of hepatic injury in GH is poorly understood. In this study, we found enhanced oxidative stress in patients with GH, as evidenced by hepatic malondialdehyde (MDA)-protein adducts and by increased oxidatively modified serum proteins. MDA-lysine epitopes and oxidatively modified serum proteins, as well as immunoglobulin G autoantibodies against MDA-lysine epitopes, were increased in untreated GH patients and to a lesser extent in GH heterozygotes compared with normal individuals. These markers of ongoing oxidative stress decreased with phlebotomy treatment in GH patients. In addition, TGF-beta1 colocalized with hepatic iron and MDA protein adducts in hepatocytes and sinusoidal cells of hepatic acinar zone 1 and normalized after iron removal. Our data suggest that iron overload increases both lipid peroxidation and TGF-beta1 expression, which together could promote hepatic injury and fibrogenesis.