We aimed to quantify fatigue frequency and evolution in amyotrophic lateral sclerosis (ALS), and to correlate fatigue with factors such as age, sex, educational level, disease duration, functionality, quality of life, dyspnoea, depression and sleepiness. Sixty ALS patients (test group: TG) selected by El Escorial criteria and 60 normal individuals (control group: CG) matched according to sex and age, were followed every three months, during 9 months, by means of self‐report scales: Fatigue Assessment Instrument (Fatigue Severity Scale plus three qualitative subscales); ALS Functional Rating Scale; McGill Quality of Life Questionnaire; dyspnoea analogical scale; Beck Depression Inventory and Epworth Sleepiness Scale. Fatigue was reported by 83% of TG (median: 3.6, interquartile range 1.5−5.4), compared with 20% of CG (median: 1, 1−1), and was significantly greater in the TG (p<0.001, Mann‐Whitney test). Fatigue severity increased by the ninth month of the study (p = 0.0008, Friedman, Müller‐Dunn post test). There was no correlation between fatigue and other parameters, except for an inverse correlation with age at disease onset (p = 0.0395, Spearman rank correlation). In conclusion, fatigue was frequent in ALS, greater in the youngest patients and worsened during follow‐up. Possibly, ALS related fatigue is an independent factor, which deserves individualized approach and treatment.