Despite a reduction in fat-free mass (FFM), a hypermetabolism has been reported with an average of 10% in amyotrophic lateral sclerosis (ALS) patients as compared with a healthy population. The objectives of this study were to confirm the level of hypermetabolism determined by using indirect calorimetry in 168 patients with a probable or a definite ALS and to study correlations with survival. Consecutive evaluations of resting energy expenditure (REE) were performed from diagnosis to the proximity of death in 44 ALS patients. Differences with the calculated value determined a ΔREE. FFM was given by bioimpedance. At T₁, REE was significantly increased by an average of 14% as compared with the calculated value. 62.3% of ALS patients were considered as hypermetabolic. REE was correlated in univariate analysis with age, sex, clinical form at onset, presence of a denutrition, weight, FFM, phase angle and ALS Functional Rating Scale (ALSFRS). In multivariate analysis, REE was linked to age and FFM. ΔREE was correlated in univariate analysis with sex, phase angle and manual muscle testing (MMT). In multivariate analysis, age and sex remained significantly correlated. During progression of ALS, REE levels remained higher than calculated values with a trend to decrease at proximity of death, whereas FFM remained stable. From T₁, survival was linked to MMT, ALSFRS, vital capacity, REE and phase angle. We confirmed the existence of a stable hypermetabolic state in ALS which depends mainly on age, sex and FFM. REE is a prognostic factor for survival in univariate analysis.