Based on the knowledge that patients with porphyria cutanea tarda (PCT) usually have chronic liver disease, several authors studied a possible relationship to hepatotropic virus infections. However, the prevalence of hepatitis B virus (HBV)-DNA by polymerase chain reaction (PCR) in serum of these patients, as well as the presence of hepatitis C virus (HCV)-RNA in paired liver, peripheral blood mononuclear cells (PBMCs), and serum samples in these patients has not been reported. We have studied 34 patients with sporadic PCT. Antibodies against HBV were detected in 91% of the patients, but in only 41% of the patients against HBV (P < .01). Viral genomes of HCV and HBV were detected in 65% and 40% of our patients, respectively (P < .05). Genomic and antigenomic HCV strands were found in liver biopsy specimens (100% and 54%), mononuclear cells (100% and 54%), and serum (45% and 0%) from 11 patients. Twelve patients were retrospectively studied, and no correlation was observed between the appearance or disappearance of viral genomes and the simultaneous presence of both genomes with the course of porphyria. In our patients with PCT, detection of viral genomes did not correlate with phlebotomy or length of time since PCT was diagnosed. Our findings demonstrate that HCV infection may be underestimated when detection is performed only in serum of PCT patients, and that HBV infection might also be increased in PCT.