A 67-year-old female noticed dyspnea on exertion associated with the development of erythema in the eyelids and the bilateral fingers, and was admitted to our hospital on July 21, 2004. Proximal muscle weakness in the limbs, heliotrope rash, and Gottron's sign were observed, but the CK level was normal (194 U/l). All autoantibodies except for rheumatoid factor were negative. Hypoxemia and interstitial pneumonia on chest CT images were observed. Based on these findings, a diagnosis of advanced interstitial pneumonia associated with dermatomyositis was made. Combination immunosuppressive therapy was initiated with corticosteroid pulse therapy and cyclosporin-A (Cy-A), resulting in marked improvement. The Cy-A trough concentration was markedly high (456.4 ng/ml). When cytomegalovirus infection developed, the dose of Cy-A was reduced. Although the blood trough concentration of Cy-A was maintained at an adequately high level, the patient died of recurrence of rapidly progressive interstitial pneumonia. Careful observation is required when the dose of Cy-A is reduced for a patient with interstitial pneumonia associated with dermatomyositis. Furthermore, it is suggested that the trough concentration level of Cy-A is not always a useful parameter.