The rapidity of progression of amyotrophic lateral sclerosis (ALS) to death or respiratory failure impacts patients, clinicians, and clinical investigators. This study compared the abilities of various pulmonary function tests to predict tracheostomy-free survival. We evaluated 95 ALS patients by determining upright and supine forced vital capacity (FVC), maximal inspiratory (MIP) and expiratory (MEP) pressures, arterial partial pressure of carbon dioxide (PaCO2), and transdiaphragmatic sniff pressures (Pdi-sniff). Tracheostomy-free survival time was measured from the date of spirometry. Supine FVC, upright FVC, MIP, MEP, and Pdi-sniff were significantly associated with tracheostomy-free survival after controlling for nonpulmonary factors, whereas PaCO2 was not. A normal supine FVC, MIP, or MEP was highly predictive for one-year survival. These tests are well suited to predict survival for trial enrollment and patient counseling. Supine FVC's simplicity of use and availability to ALS investigators makes it a particularly attractive predictor of one-year survival in ALS.