We examined conjugal and blood relatives of one kindred for evidence of porphyria cutanea tarda. The disease was identified in eight family members in three generations. Four were classified as having overt porphyria cutanea tarda because of four criteria: photo-enhanced dermatosis; excessive urinary excretion of uroporphyrins; characteristic thin-layer chromatographic pattern of urinary porphyrins; and decreased activity of erythrocyte uroporphyrinogen decarboxylase. Two patients with excessive excretion of uroporphyrins or characteristic chromatograms, or both, and decreased uroporphyrinogen decarboxylase activity were classified as having subclinical porphyria cutanea tarda, and two with decreased uroporphyrinogen decarboxylase activity only were classified as having latent porphyria cutanea tarda. This study provides further evidence that prophyria cutanea tarda can be a familial disease inherited in an autosomal dominant fashion. We propose a reclassification of porphria cutanea tarda as an overt, subclinical or latent disorder.