Granulomatous hepatitis and fever of unknown origin. An 11-year experience of 23 cases with three years' follow-up. Granulomatous hepatitis is a common cause of fever of unknown origin in up to 13% of patients with prolonged fever. Attempts to define an exact etiology of the granulomatous hepatitis frequently does not yield a precise diagnosis, so that the physician must consider empiric treatment. In this paper we retrospectively review 23 patients in whom granulomatous hepatitis was found as part of the initial assessment of fever of unknown origin, and we report on their outcomes after an overall prospective follow-up of 37 months. In 26% a precise diagnosis was established at the time of assessment: Q-fever in three, mycobacterial disease in two, and histoplasmosis in one. In the remaining 74% no etiology was established after 44 months follow-up. Forty-one percent of the idiopathic group resolved spontaneously without therapy, and 18% received short-term prednisone or indomethacin with a favourable outcome. The remaining 41% required long-term prednisone therapy for a mean of 33.1 months, but all have remained afebrile and otherwise healthy after 59.6 months follow-up. We conclude that patients with fever of unknown origin who are diagnosed as having idiopathic granulomatous hepatitis have an excellent prognosis, even the minority who require long-term corticosteroids. 