Mental Disorders Mental disorders are psychological and behavioral syndromes that deviate significantly from those typical of human beings enjoying good mental health. In general, a mental disorder involves present distress or impairment in important areas of functioning. Such deviations in thought, feelings, and behavior have been recognized throughout history in all cultures. For the greater part of recorded history, mental deviations were considered supernaturally or unnaturally caused, the work of evil spirits or human depravity. After small beginnings in the 16th and 17th centuries, however, the mental science that eventually developed into psychiatry acquired respectability