Weight loss is increasingly considered as a negative prognostic marker in amyotrophic lateral sclerosis (ALS). Despite the critical importance of nutritional issues in ALS, and the common use of percutaneous endoscopic gastrostomy (PEG), there is a general lack of knowledge on peri-interventional treatment, optimal parameters of enteral nutrition, its timing during disease progression and its potential disease-modifying effects in ALS patients. Here we report the results of a multi-center prospective study of percutaneous endoscopic gastrostomy (PEG) in ALS. In this observational clinical trial, 89 ALS patients were prospectively enrolled over a 3-year period and longitudinal data were collected over 18 months. PEG was a safe procedure even in patients with low forced vital capacity, and prophylactic single-shot antibiosis as well as slow increase of caloric nutrition via PEG was beneficial to avoid complications. No signs of refeeding syndrome were observed. High-caloric intake (>1,500 kcal/d) via PEG in patients that lived at least 12 months after PEG insertion was correlated with prolonged survival. Additional oral food intake was not associated with a worse prognosis. Our results suggest that peri-interventional PEG management should include prophylactic single-shot antibiosis, slow increase of caloric intake, and long-term high-caloric nutrition. Although our results indicate that PEG might be more beneficial when applied early, we believe that it can also be performed safely in patients with far advanced disease. Because of its explorative and observational character, most of our results have to be confirmed by a randomized interventional trial.