The impact of noninvasive positive‐pressure ventilation (NIPPV) on pulmonary function studies, quality of life, and survival was assessed in patients with amyotrophic lateral sclerosis. NIPPV did not change the rate of decline of the forced vital capacity (FVC) and forced expiratory volume in the first second (FEV₁) (2.31 and 2.09 percent‐predicted points per month, respectively). NIPPV resulted in a drop of FEV₁ by 5.94 percent‐predicted points (P = 0.07), and of maximal inspiratory pressure by 6.33 percent‐predicted points (P = 0.11). The change in FEV₁ and FVC pre‐ and postintervention correlated with the corresponding change in maximal inspiratory pressure. Fatigue and mastery scores were improved by NIPPV. Median survivals in patients intolerant and tolerant of NIPPV were 5 and 20 months, respectively (P = 0.002). Although NIPPV has no impact on the rate of decline of lung function and may have deleterious effects on spirometric measures, it may improve quality of life and survival. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 403–409, 2001.