We report five cases of biopsy-proven hepatitis developing between six and 20 weeks after administration of diclofenac. In one patient jaundice had previously developed following use of ibuprofen. In another the clinical, biochemical and histopathological features were those of chronic active hepatitis and treatment with corticosteroids was required. All patients recovered from their liver injury without sequelae. Resolution of symptoms occurred between three and 12 weeks following cessation of the drug, while liver function tests returned to normal between seven and 16 weeks after drug withdrawal, except in the patient with chronic active hepatitis who remained biochemically abnormal for eight months. Three of the five patients developed transient circulating autoantibodies, suggesting immune mechanisms may be important in the pathogenesis of this injury. The incidence of severe hepatic dysfunction related to the use of diclofenac appears low and is probably in the order of one case per 50-100,000 prescriptions.