Liver granulomas have long been known to pose diagnostic problems for pathologists; however, their prevalence and associated etiologic factors have not been studied in liver transplant patients. We reviewed 3632 liver biopsy specimens from 563 patients at two institutions and identified 42 patients with posttransplant granulomas. A possible or probable etiologic factor was identified in 30 (71%) cases. Most were epithelioid granulomas and microgranulomas located in the parenchyma associated with hepatocyte necrosis (21 cases, 50%). Portal-based granulomas were associated with recurrent primary biliary cirrhosis (5 cases, 12%), acute cellular rejection (2 cases, 4.8%), and a foreign body-type reaction (1 case, 2.4%). One case was associated with tuberculosis (2.4%), 4 cases occurred in a fatty liver (9.5%), and 8 patients had liver granulomas but no other significant abnormality. The granulomas were most frequent in the first 7 months after transplantation when the patients were biopsied more often and underwent episodes of rejection or acute hepatitis. Portal-based granulomas in this period were usually associated with acute cellular rejection. After 7 months, the frequency of granulomas as well as the number of biopsies decreased and portal-based granulomas associated with recurrent primary biliary cirrhosis were most common (5 cases, 12%). Rare, late-appearing parenchymal granulomas were also seen (3 cases) and consisted of 1 lipogranuloma and 2 cases of epithelioid granuloma. The latter were thought, in 1 patient, to be associated with parenchymal hepatocyte necrosis; the others were of unknown etiology.