Studies have suggested that obesity is associated with better prognosis among individuals with various types of neurodegenerative diseases, and while some studies suggest that the same is true of amyotrophic lateral sclerosis (ALS), other works cast doubt on this conclusion. Therefore, we conducted a meta-analysis to systematically evaluate the role of body mass index in the prognosis of ALS. PubMed was systematically searched to identify eligible articles, and data on long-term survival were meta-analyzed in terms of hazard ratios (HR) with corresponding 95% confidence intervals (CI). Level of heterogeneity among studies and publication bias were estimated. A total of 17 studies with 9991 ALS patients were included in the review. Each increase of 1 kg/m2 in body mass index was associated with significantly better long-term overall survival (HR 0.95, 95%CI 0.93–0.97; p < 0.001). Obesity may also be a strong predictor of favorable long-term prognosis (HR 0.73; 95%CI 0.62–0.86; p < 0.001). Our results suggest that higher body mass index and obesity are associated with better long-term survival of ALS patients. © 2019, © 2019 World Federation of Neurology on behalf of the Research Group on Motor Neuron Diseases.