Huntington's disease is an inherited neuropsychiatric disorder characterized by a triad of symptoms: motor, cognitive and psychiatric. Psychiatric symptoms occur prior to the motor symptoms in approximately 50% of the cases, and knowledge of the psychiatric symptoms is essential in making an early diagnosis. In this article, we argue that further knowledge of the genetic background of Huntington's disease may contribute to a better understanding of the polygenetic psychiatric diseases such as schizophrenia and bipolar affective disorder.