This study was carried out on 40 patients with various neuromuscular disorders and 20 healthy controls. Patients were divided into three groups according to muscular weakness into grade III, IV and V. The following measurements were obtained for control subjects and all patients: Forced vital capacity (FVC), forced expiratory volume in the first second (FEV1) expressed as ٪ of predicted, PImax and PEmax. Also sleep apnea detection for 10 patients with low values for these parameters was done with arterial blood gas analysis. This study demonstrated that there was a significant reduction of FVC٪ in grade III and IV, FEV1٪ and PImax was significantly reduced in grade III only but PEmax was significantly reduced in grade III, IV and V. Sleep apnea detected in 5 patients subjected to sleep study and the blood gas parameters remained in the normal range in the studied patients for sleep apnea. We conclude that study of ventilatory functions, maximal inspiratory and expiratory pressures are a useful diagnostic tools for early detection of pulmonary dysfunction and reduction in maximum expiratory pressure is the first sign of dysfunction.