Chronic hypertension with renal failure is the most common cause of death in a large family (10 children, 40 grandchildren, 109 great-grandchildren) with acute porphyria. A prospective study of 26 porphyric (19 latent) and 26 nonporphyric subjects shows a significant difference between mean systolic (141 versus 123 mmHg, P < 0.05) and diastolic (88 versus 74 mmHg, P < 0.05) blood pressures and plasma creatinines (geometric mean 99 versus 79 mmol/l, P < 0.02). Five of the 19 porphyric grandchildren have died of the complications of chronic hypertension, with renal failure in three. When the results of the retrospective and prospective studies in these 19 subjects are combined, 10 of the 16 tested (62%) had hypertension and seven of the 14 tested (50%) had renal impairment. Neither hypertension nor renal failure are known to affect the 21 grandchildren who were either not porphyric or of unknown status. This family provides a unique opportunity to study these common but little reported sequelae of acute porphyria. These complications affect subjects with latent porphyria as well as those who have experienced clinical attacks.