Social cognition can be impaired in a range of neuro-degenerative conditions, yet the impact of these difficulties on behaviour and social relationships is not yet fully understood. This study assessed social cognition in 27 participants with Dementia of the Alzheimer Type (DAT) and their co-residing partners (N = 27) and explored the relationships between social cognition, cognitive ability, relationship continuity and behaviour following diagnosis. In line with previous research, participants with dementia scored lower on social cognition tasks compared to their partners. Behaviour changes such as apathy, disinhibition and agitation in participants with dementia were significantly related to relationship continuity; however, no significant associations were found with measures of social cognition. The results of this study are discussed within a therapeutic context and in line with current guidelines and policies.