The most effective treatment of chronic hepatitis B virus (HBV) infection is interferon alfa (IFN-α), a potentially severe side effect of which is the induction of autoimmunity. To assess whether IFN- α causes clinical or serological autoimmune manifestations, we studied 61 children randomized to receive 5 MU/m2 of IFN-α three times per week for 12 weeks, with or without steroid priming or no treatment. Autoantibodies to antinuclei (ANA), smooth muscle (SMA), gastric parietal cell (GPC), liver kidney microsomal type 1, mitochondrial, liver cytosolic antigen, thyroid microsomal, and thyroid globulin were detected by standard techniques. Over a median of 4 years (range, 1-5 years) from randomization, no clinical signs of autoimmunity were observed. Autoantibody positivity for nuclei, smooth muscle, and/or gastric parietal cells was observed on at least one occasion in 42 of 61 children (69%), with no overall difference in the prevalence between patients treated with interferon alone (19 of 24 [79%]), steroids plus interferon (13 of 20 [65%]), or untreated controls (10 of 17 [59%]). There was also no difference in the autoantibody prevalence before, during, and at follow-up after cessation of treatment in both interferon-treated and interferon- untreated patients. Autoantibodies are common in chronic HBV infection, and their prevalence is uninfluenced by IFN-α.