Personality refers to the innate and enduring characteristics that influence an individual’s attitudes, behaviours, and experience of themselves, others, and the world. Historically, personality disorders were conceptualised as enduring and pervasive disturbance in an individual’s patterns of thinking, feelings, and behaviours. This disturbance results in significant disturbance in their psychosocial functioning and interpersonal relationships The diagnosis of personality disorders in people with intellectual disability can be a contentious issue. The chapter presents an overview of the condition, the treatments with medication available, and their relevance.

Other categories of personality disorders, apart from borderline personality disorder are encountered in clinical practice and these are described and named in DSM-5 but not in ICD-11. The clinical features and diagnostic criteria of all these types are reviewed here. They are grouped into three clusters: Cluster A, the eccentric PDs – which include paranoid, schizoid and schizotypal PDs – and Cluster B, the dramatic group. The most important of these is antisocial personality disorder as well as borderline and histrionic PDs. Cluster C, which are the avoidant or fearful PDs, include avoidant, dependent and obsessive-compulsive types.

Also included in this chapter are a category of conditions known as ’impulse disorders’, where subjects experience an impulse to commit some action which may give them pleasure and are said to be ego-syntonic, yet result in distress to the individual or harm to others. These include gambling, gaming disorder, intermittent explosive disorder, kleptomania and pyromania.