In this study, 100 hemodialyzed patients were examined for pseudo-porphyria cutanea tarda, which was first described in 1975. Pseudo-porphyria cutanea tarda was found in 16%. Our main concern was the analysis of the etiological factors; none of the hypotheses so far put forward--a medicinal agent, an hepatic disorder, or some factor relating to the material used in the dialysis--has been confirmed. On the other hand, this condition occurred in patients with the longest interval since dialysis, and who were more often than not completely anuretic. These facts would seem to indicate that this is part of a premature ageing process which is common in these patients.