Our objective was to compare the cognitive and behavioural profile of patients with amyotrophic lateral sclerosis (ALS) and behavioural variant frontotemporal dementia (bvFTD), and to explore the continuum between these disorders according to neuropsychological and behavioural performance using novel methods of testing and analysis. Twenty patients with ALS, 20 bvFTD patients and 20 healthy controls completed a neuropsychiatric and neuropsychological assessment including cognitive screening, working memory, inhibitory control, decision making and emotion recognition. The resulting neuropsychological and behavioural data were analysed by Rasch analysis. ALS patients showed a similar profile to bvFTD patients on tests of working memory, inhibitory control and behavioural measures. Nine ALS patients (45%) had cognitive impairment and five (25%) met criteria for bvFTD. Even in a subset of MND patients with no impairment on the ACE-R, subtle impairment of inhibitory control together with moderate to severe apathy, were found. The Rasch analysis confirmed that all patients could be ranked on the same continuum, based on their neuropsychological performance and behaviour. Thus, the cognitive and behavioural profiles of ALS mirror those seen in bvFTD. Impaired inhibitory control and behavioural changes suggest subtle orbitofrontal dysfunction in ALS. The Rasch analysis revealed a clear overlap between bvFTD and ALS.