The concept of neuroticism as a temperament can be traced back to the ancient Greek physicians Hippocrates and Galen. Their descriptions of the melancholic temperament included symptoms of depression and anxiety and social withdrawal. Both attributed the disorder to both an organic basis (an excess of black bile) and to an environmental one. Hippocrates said that melancholia could be precipitated by loss of love or conflict and guilt, whereas Galen, anticipating Freud by 18 centuries, suggested it could be due to blocked sexual outlet. In his early theory, Freud also ascribed pure anxiety states (panic disorder) to the tension generated by sexual frustration.

Freud regarded neurosis on a continuum lying between neurotic character and psychosis, depending on the extent of regression due to conflict between ego and id impulses. The concept of neurosis as a disorder suggested that it could be a temporary condition rather than a basic personality dimension. Freud included hysteria among the psychoneuroses, attributing differences between it and disorders such as anxiety and obsessive-compulsive to different levels of psychosexual fixation.

During the 19th century, a number of psychiatrists, including Jung, distinguished between “psychasthenic” and hysterical disorders on the basis of a second dimension of personality, extraversion-introversion. Eysenck (1947), whose early research used mental patients as subjects, regarded the “dysthymic” (anxious and depressed) types as introverted neurotics, and the hysteric and psychopathic types as extraverted neurotics. He defined neuroticism as a basic dimension of personality that could be regarded as going from extreme emotional stability at one end to emotional instability at the other.