Abstract This chapter covers neuropsychiatry in the medical sense (behavioural neurology and neuropsychiatry). Starting with the psychiatric presentations of organic illness and neurological examinations and investigations in psychiatry, it covers movement disorders, neurodevelopmental disorders, epilepsy, Parkinson’s disease and other related syndromes, and the psychiatric effects of central nervous system infections and human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS). Outlining both the aetiology and treatment for dementia and Alzheimer’s disease, other specific neurodegenerative conditions are also featured.