In many countries hepatitis C virus infection has been considered a major factor triggering overt porphyria cutanea tarda. The prevalence of hepatitis C virus infection was retrospectively studied in 87 patients who during a period of 11 years were diagnosed with porphyria cutanea tarda in Stockholm. Among patients with the sporadic form of porphyria cutanea tarda, the prevalence of hepatitis C virus infection was 36.4%. As hepatitis C virus infection may today be successfully treated and as the infection may be clinically silent and thus unknown to the patient, it is important to screen all patients with porphyria cutanea tarda for hepatitis C virus infection.