In order to assess the incidence of hepatocellular carcinoma (HCC) in porphyria cutanea tarda (PCT), 83 patients (77 males, 6 females, mean age 57.4 years) were studied. Thirteen patients (15.7%) had HCC, all of whom were male and cirrhotics with a mean age of 58.5 years. HCC patients showed a statistically significant (P < 0.0005) longer evolution time (23 years since onset of the cutaneous disease) than patients without HCC (9.4 years), while the age of onset was similar in both groups. Differences in alcohol intake and hepatitis B virus (HBV) markers were non-significant, although high prevalence (54%) of past HBV infection was found in both groups. In HCC development, attributable risks of 100% were found for cirrhosis (P < 0.001), male sex (P = NS) and for age over 51 (P < 0.025). Therefore, PCT harbours a high incidence of HCC; evolution time, cirrhosis and age over 51 appear to be the most important contributing factors.