Autoimmunity and high rates of autoantibodies have been implicated in the pathogenesis of porphyria cutanea tarda. These abnormalities could be in part virus-induced, since porphyria cutanea tarda in most geographical regions is highly associated with hepatitis C virus infection. We analyzed the link of autoantibodies, autoimmune hepatitis and systemic lupus erythematosus in 111 patients with porphyria cutanea tarda and sex- and age-matched controls (mean age 58+/-13 years) in Germany, a region with a low prevalence of hepatitis C virus infection. Patients with porphyria cutanea tarda displayed lower rates of anti-nuclear antibodies (16/111, 14% vs 28/111, 25%, p<0,05) and of antibodies against smooth muscle (25/111, 23% vs 48/111, 43%, p<0,01), than controls. The percentage of patients with porphyria cutanea tarda with positive anti-HCV was low but significantly higher than in our controls (9/111, 8% vs 0/111, 0%, respectively), (p<0,05). Two patients with porphyria cutanea tarda (2/111, 2%) fulfilled the criteria for systemic lupus erythematosus and not one of 65 patients was found to have clinical autoimmune hepatitis. In the first controlled study of a large cohort of patients with porphyria cutanea tarda no increased prevalence of selected autoantibodies and autoimmune hepatitis was found. However, a higher prevalence of HCV infection and systemic lupus erythematosus in patients with porphyria cutanea tarda was confirmed.