In a study designed to assess personality patterns of patients with chronic insomnia, a total of 528 subjects (428 insomniacs and 100 controls) completed the Minnesota Multiphasic Personality Inventory (MMPI). Comparison of the MMPI profiles of insomniacs from a semirural area and of those from an urban area, each in a completely different geographic region, showed results consistent for high levels of psychopathology as well as for specific personality patterns within and between groups. The personality patterns of insomniac subjects were remarkably homogeneous: only a few MMPI code types accounted for about one-half of each insomniac sample. The insomniac profiles were consistently characterized by the presence of neurotic depression, rumination, chronic anxiety, inhibition of emotions, and an inability to discharge anger outwardly. The results of this study confirm the original hypothesis that the handling of stresses and conflicts through an internalization of emotions leads to physiologic activation and is a major factor underlying the development and maintenance of chronic insomnia.