Percutaneous endoscopic gastrostomy (PEG) is a standard procedure for feeding dysphagic amyotrophic lateral sclerosis (ALS) patients. Nevertheless, the effect of prognostic factors influencing survival after PEG remains unclear. We aimed to evaluate the prognostic value of several clinical features on survival after PEG placement. This study investigated 151 patients with ALS, in whom a PEG was inserted over the last 16 years in our centre. Survival curves were determined by Kaplan-Meier and the analysis of potential prognostic factors was performed by a Cox regression model. The overall median survival was 32 months, longer in spinal-onset disease patients - 42 vs. 29 months in bulbar-onset patients (p < 0.001). Median survival after PEG placement was 7.5 months, similar in both bulbar- and spinal-onset patients, 7.9 vs. 7.1 months, respectively. Thirteen percent of patients died within one month after PEG placement; this short-term survival was influenced by low forced vital capacity (FVC < 50%). In a multivariate analysis, only older age at disease onset was independently associated with poor outcome after PEG placement. In conclusion, survival after PEG placement was similar in bulbar- and spinal-onset patients, suggesting that the latter were in a more advanced stage at the time of PEG placement. Low FVC was associated with higher risk of short-term mortality. Older age at disease onset was associated with poorer outcome in bulbar-onset patients. Younger bulbar-onset patients are those who benefited most from PEG.