Cystic fibrosis (CF) is the most common, life-shortening genetic disease in Caucasians. The vast majority of patients die from cardiorespiratory failure. Although most patients now live into early adulthood, a third will die before their 21st birthday. Noninvasive positive pressure ventilation (NIPPV) has been used effectively to treat respiratory failure in adults with chronic lung disease. However, there have been no controlled, prospective studies of the use of NIPPV in delaying the onset or progression of chronic respiratory failure in children with CF. We hypothesize that early intervention with noninvasive positive pressure ventilation improves daily function and quality of life, and delays the onset of respiratory failure, in patients with cystic fibrosis. Specifically, in children and adolescents with severe CF-related lung disease treated with NIPPV, compared to matched controls, we predict (1) An improvement in respiratory function, as evidenced by a slower rate of decline of pulmonary function tests, better exercise tolerance, improved ventilatory muscle endurance and improved gas exchange during wakefulness and sleep; (2) An improvement in nutritional and metabolic status, as evidenced by weight gain and a decreased resting energy expenditure; and (3) Improved quality of life, better quality of sleep and a decreased number of pulmonary exacerbations. This study will be the first to use a prospective, randomized, double-blinded design to comprehensively evaluate the effects of NIPPV in pediatric patients with CF. In keeping with the mission of the RFA, this study will use a multidisciplinary approach to improve management and enhance the quality of life in children with chronic respiratory failure.