A 51 year-old woman underwent living related renal transplantation under cyclosporine A immunosuppression, After surgery, she did well initially, but the serum creatinine level subsequently rose to 3,6 mg/dL on postoperative day 95, she was admitted at Severance Hospital for further evaluation. On admission day 4, a renal biopsy was performed, and the microscopic findings revealed an interstitial mononuclear cell infiltrate, suggestive of severe allograft rejection. Because of persistently impaired renal function, the patient was began on twice weekly demooialysis, and the progression of renal deterioration paralleled the onset of a thrombocytopenia. The platelet count dropped to 13×109/L despite daily platelet transfusion. On admission day 19, antiplatelet antibody against the glycoprotein Ib/IX (GP Ib/IX) and glycoprotein Ⅱb/Ⅲa (GP Ⅱb/Ⅲa) complex was detected in the presence of cyclosporine A (CsA) with modified antigen capture ELISA (MACE) assay, thereby implicating the drug. CsA was stopped immediately and immunosuppression drug was changed to FK506. After CsA was discontinued 7 day later, her platelet count returned to normal, up to 170× 109/L without requirement of any platelet concentrates. This paper presents the first case of CsA induced thrombocytopenia in Korea which was confirmed by in vitro CsA dependent antiplatelet antibody detection test.