Immune thrombocytopenic purpura (ITP) is a rare complication after liver transplantation. Infection with cytomegalovirus (CMV) is a frequent complication of organ transplantation and may induce autoimmune diseases, such as ITP. We report a case of ITP after primary CMV infection in a 3-year-old boy recipient of living-related orthotopic liver transplantation (OLT). The ITP developed 2 years after OLT in this patient who had received tacrolimus as an immunosuppressive agent, with nadir platelet counts of 5000/mm3 in 2 weeks. The patient was treated with two courses of intravenous gamma globulin (1 g/kg/day for 2 days) and subsequent oral prednisolone (1.3 mg/kg/day for 2 weeks). He recovered from thrombocytopenia 4 weeks later. An inadequate immunosuppression, as evident by the low serum tacrolimus level (5.8 ng/mL before the episode of ITP) in this patient, may allow the development of ITP after CMV infection. [J Formos Med Assoc 2007;106(4):327-329]