The subject of Inappropriate Sexual Behaviour (ISB) amongst clients with neurological impairment, specifically Acquired Brain Injury (ABI) and dementia, has received limited coverage to date within the literature. This paper discusses some of the problems encountered in the definition and quantification of ISB, in particular the absence of standardized measurement tools to record ISB within an inpatient setting. Whilst ISB is reported to be less prevalent than other behavioural sequelae of brain injury or dementia, it is suggested that its impact on patients and carers can be significant. Ill-defined terminology and the absence of relevant assessment tools add to the specific challenges of understanding and managing ISB within a care or rehabilitation setting. As a result, it is argued that the subjective attitudes of staff and the culture of an institution can dominate the approach taken to dealing with ISB for these client groups.