Fifty male subjects were group-matched for age and socioeconomic status. Twenty of the subjects were diagnosed as having sleep apnea and 20 were diagnosed as having narcolepsy on the basis of sleep studies. The remaining 10 subjects served as normal controls. Differences among the groups were evaluated on the bases of two psychological instruments designed to assess personality characteristics and mood states. The findings suggest that narcoleptics and apneics both present discriminatively different psychological profiles than do normals. Moreover, personality characteristics of these two groups are distinguishable from one another. Apneics tend to be individuals with hypochondriacal and hysterical characteristics, whereas narcoleptics are more easily characterized by anxiety and social introversion. Both severity of psychological disturbance (mean Minnesota Multiphasic Personality Inventory elevations) and personality pattern (two-point codes) distinguish the groups. Key Words: Sleep apnea-Narcolepsy-Psychological profiles.