We report the case of a patient in whom amitriptyline administration for 5 wk was followed by prolonged cholestasis. Jaundice and pruritus lasted 19 and 20 mo, respectively. Three liver biopsies were performed at different stages of the disease showing the course of liver lesions. Cholestasis initially located in the region of the hepatic venule came to be associated with the progressive development of portal tract lesions consisting of inflammatory infiltration, fibrosis, and disappearance of interlobular bile ducts. Amitriptyline hydroxylation and dextromethorphan O-demethylation are deficient in subjects with the poor metabolizer phenotype of debrisoquine. Drug oxidation phenotyping with dextromethorphan showed that this patient had the extensive metabolizer phenotype. This observation demonstrates that amitriptyline can induce prolonged cholestasis and suggests that the susceptibility to develop liver injury while taking this drug may not be related to a genetic deficiency of its hydroxylation.