Among the different types of hepatic porphyrias, acute intermittent porphyria (AIP) and the group of chronic hepatic porphyrias (CHP) are most frequently seen in Europe. Both diseases are supposed to be inherited, but clinical manifestation mostly occurs following endogenous and especially exogenous stimulation. While recurrent attacks of abdominal and neuropsychiatric symptoms in AIP are frequently precipitated by therapeutic doses of commonly used drugs, the gradual development of porphyria cutanea tarda (PCT) from a clinically non-apparent type of CHP seems to be most commonly due to excessive and prolonged intake of alcohol. The characteristic and with regard to the laboratory findings important pathobiochemical features, the clinical symptoms, and the present therapeutic concepts of both disorders of hepatic porphyrin metabolism are discussed. The prognosis of hepatic porphyrias will be determined above all by early diagnosis of the metabolic disorder as well as by a profound medical information of the patient to avoid strictly all well-known exogenous factors which may initiate or exacerbate the disease.