Introduction: This study aimed to determine the prognostic factors and the values that predict survival after percutaneous endoscopic gastrostomy (PEG) tube placement in patients with amyotrophic lateral sclerosis (ALS). Methods: We retrospectively analyzed the correlations for 97 consecutive patients with ALS between clinical parameters and survival following PEG tube placement using the log-rank test and Cox proportional-hazards models. Results: The log-rank test showed that an arterial carbon dioxide pressure (PaCO2) of <= 40 mmHg (P = 0.0054), a forced vital capacity (FVC) of >= 38% of predicted (P = 0.0003), and bulbar-onset (P = 0.0121) were significantly associated with better post-PEG survival. Multivariate analysis showed that the FVC and PaCO2 were associated with better post-PEG survival (P = 0.0081 and P = 0.0265, respectively). Conclusions: PEG tube placement in ALS is recommended when FVC is >= 38% of predicted and when PaCO2 is normal.