ObjectiveIn 2017, the diagnostic criteria for cognitive and behavioural impairment in amyotrophic lateral sclerosis (ALS) with frontotemporal dementia (ALSFTD-1) have been modified (ALSFTD-2) with the inclusion of a novel category (ALS with combined cognitive and behavioural impairment, ALScbi) and with changes of operational criteria of the other categories (ALS with cognitive impairment (ALSci), ALS with behavioural impairment (ALSbi) and ALS with frontotemporal dementia (ALS-FTD)). We compared the two sets of criteria to assess the effect of the revised criteria on the cognitive classification of patients with ALS.MethodsTwo cohorts of patients with ALS were included in this study: a population-based cohort including patients identified through the Piemonte/Valle d’Aosta register for ALS in the 2014–2017 period (n=321), and a referral cohort recruited at the Turin ALS centre and at the ALS centre of the Maugeri Institute in Milan in the same period (n=205). Cognitive function was classified in blind by two neuropsychologists expert in ALS.ResultsALSFTD-2 criteria determined a shift of about 15% of patients from their original category to a new one. In both cohorts, about 9% of patients were reclassified to the novel category ALScbi. Among patients previously classified as cognitively normal, 14 (4.3%, population-based cohort) and 19 (9.3%, referral cohort) were reclassified as ALSbi or ALSci. The median survival of the different categories was significantly different with both with sets of criteria.ConclusionsThe new ALSFTD-2 criteria, compared with the old ones, have positive effects on the clinical practice being more sensitive to the early cognitive impairment and having a better prognostic yield.