Within the "primary" cholestasis we can discriminate "essential" forms due to an endogenous biochemical error of bile acid metabolism and/or secretion and "conditioned" forms, in which a known precipitating factor is required to elicit the functional disorder responsible for cholestasis. Among the essential forms of cholestasis must be included benign recurrent intrahepatic cholestasis or Summerskill-Walshe disease, Aagenaes disease, progressive familial intrahepatic cholestasis or Byler's disease, and forms due to disorders of the peroxisomes. Benign recurrent intrahepatic cholestasis, the best known form, is characterized by recurrent episodes of itching and jaundice with an acute onset separated by symptom-free intervals, which shows no tendency to progress to liver failure. The conditioned cholestasis group comprises cholestasis of pregnancy and drug-induced cholestasis. Benign recurrent cholestasis of pregnancy is a form induced "by" pregnancy and not a form occurring "in" pregnancy, such as cholestasis due to hepatitis, to primary biliary cirrhosis, to cholelithiasis. Drug-induced cholestasis is a chapter of great clinical relevance: forms due to steroid hormones and due to phenothiazines are discussed.