BACKGROUND AND OBJECTIVE: Porphyria cutanea tarda (PCT) is a disorder of porphyrin metabolism associated with decreased activity of uroporphyrinogen decarboxylase (URO-D) in the liver. The relevance of iron in the pathogenesis of PCT is well established: iron overload is one of the factors that trigger the clinical manifestations of the disease and iron depletion remains the cornerstone of therapy for PCT. A role for genetic hemochromatosis in the pathogenesis of iron overload in PCT has been hypothesized in the past but only after the recent identification of the genetic defect causing hemochromatosis has the nature of this association been partially elucidated. This review will outline current concepts of the pathophysiology of iron overload in PCT as well as recent contributions to the molecular epidemiology of hemochromatosis defects in PCT. EVIDENCE AND INFORMATION SOURCES: The authors of the present review have a long-standing interest in the pathogenesis, etiology and epidemiology of iron overload syndromes. Evidence from journal articles covered by the Science Citation Index(R) and Medline(R) has been reviewed and collated with personal data and experience. STATE OF THE ART AND PERPECTIVES: Mild to moderate iron overload plays a key role in the pathogenesis of PCT. The recent identification of genetic mutations of the hemochromatosis gene (HFE) in the majority of patients with PCT confirms previous hypotheses on the association between PCT and hemochromatosis, allows a step forward in the understanding of the pathophysiology of the disturbance of iron metabolism in the liver of PCT patients, and provides an easily detectable genetic marker which could have a useful clinical application. Besides the epidemiological relevance of the association between PCT and hemochromatosis, however, it remains to be fully understood how iron overload, and in particular the cellular modifications of the iron status secondary to hemochromatosis mutations, affect the activity of URO-D, and how the altered iron metabolism interacts with the other two common triggers for PCT and etiological agents for the associated liver disease: alcohol and hepatitis viruses. The availability of a genetic marker for hemochromatosis will allow some of these issues to be addressed by studying aspects of porphyrins and iron metabolism in liver samples obtained from patients with PCT, liver disease of different etiology and different HFE genotypes, and by in vitro studies on genotyped cells and tissues.