This study presents the Edinburgh Cognitive and Behavioural ALS Screen (ECAS), developed for ALS patients with physical disability for use by health care professionals. The screen is designed to detect the specific profile of cognition and behaviour changes in ALS and to differentiate it from other disorders. Forty-eight ALS patients (none with evident dementia), 40 healthy controls and 20 carers were recruited. The ECAS, a 15-20-min screen, includes an ALS-Specific score (executive functions and social cognition; fluency; language); an ALS Non-specific score (memory; visuospatial functions); and a carer behaviour screen of five domains characteristic of frontotemporal dementia (FTD). Data from healthy controls produced abnormality cut-offs of 77/100 ALS-Specific score; 24/36 ALS Non-specific score; 105/136 ECAS Total. Twenty-nine percent of patients showed abnormal ALS-Specific scores, and 6% also showed abnormal ALS Non-specific scores. The most prevalent deficit occurred in language functions (35%) followed by executive functions and fluency (23% each). Forty percent of carers reported behaviour change in at least one domain, while 15% met criteria for possible FTD. In conclusion, the ECAS is an effective within-clinic assessment for ALS that determines the presence, severity and type of cognitive and/or behavioural changes, an essential first step to managing these symptoms.