We report a patient of polymyositis and myasthenia gravis as manifestations of chronic graft-versus-hot disease (GVHD). A 48-year-old man was diagnosed as having chronic myelogenous leukemia at the age of 42 years, and had bone marrow transplantation (BMT) two years after the onset of the disease. Since he suffered from mild liver dysfunction and cutaneous involvement manifesting chronic GVHD, he was placed on prednisolone and cyclophosphamide. As his condition improved, the prednisolone was gradually tapered. Forty-one months after the BMT, the patient developed muscle pain and muscle weakness. A diagnosis of polymyositis was made from muscle biopsy and laboratory findings. An increase in the prednisolone dose was effective but a few weeks later the patient noticed ptosis and recurrence of muscle weakness. A tensilon test and anti-acetylcholine receptor antibody produced positive results, leading to a diagnosis of myasthenia gravis. Only one case of polymyositis and myasthenia gravis as manifestations of chronic GVHD has been reported, and in our patient both symptoms appeared almost at the same time. Although neuromuscular symptoms as a manifestation of chronic GVHD are rare, all patients receiving BMT should be carefully followed up neurologically to detect neuromuscular complications.