Respiratory failure and pulmonary infection are the major causes of death in the Duchenne muscular dystrophy patients. The purposes of this study are to evaluate pulmonary function of Duchenne muscular dystrophy patients, to verify usefulness of the measurements of maximum static pressures and to define functional classes in Duchenne muscular dystrophy patients. Forty two Duchenne muscular dystrophy patients were assessed for pulmonary function by a routine pulmonary function test and the measurements of maximum static pressures. This study showed significant negative correlations between the subject's functional class and the values of forced vital capacity(FVC), maximum inspiratory and expiratory pressures(MIP and MEP). Significant reduction of maximum static pressures began earlier than FVC in the course of disease. The MEP was as low as 64% of the predicted value before FVC and MIP showed demonstrable decline. A pulmonary care program focusing on maintaining adequate respiratory pressures is suggested to start early for the child with Duchenne muscular dystrophy.