We investigated the utility of the Cambridge Behavioural Inventory (CBI), a carer-completed questionnaire, in a large cohort with Parkinson's disease (PD) (n = 215). In a sub-cohort of 112 patients with PD, the CBI was found to be a valid instrument compared with the Neuropsychiatric Inventory, PDQ-39 and UPDRS, with high internal consistency. Furthermore, in the whole cohort, the CBI was sensitive to changes in behaviour with disease progression. Comparison between CBI scores in PD and other neurodegenerative diseases, including Huntington's disease (HD) (n = 75), Alzheimer's disease (AD) (n = 96) and frontal variant frontotemporal dementia (fvFTD) (n = 64), revealed distinct profiles for each disease. Predominant deficits were "sleep"' and "self care" in PD; "memory" in HD and AD; and "motivation" and "stereotypic behaviours" in fvFTD. The CBI is a robust, easy-to-use and valid instrument, which has the capacity to discriminate between neurodegenerative diseases, and may be of value in monitoring therapeutic interventions.