(1) Delirium occurred somewhat more frequently among patients in a psychopathic hospital than among normal people of the same age; the difference, however, is slight and suggests that delirium is a very distinct entity, probably different from the usual diseases seen in a psychopathic hospital. In this study no proof was obtained regarding the relationship between the economic and social dependency and the incidence of delirium.(2) Despite the psychopathological phenomena observed in aviators who fly above their ceiling, normal people living an average of 31 years at Leadville, Colorado (altitude 10,200 feet), gave histories of less delirium than normal individuals having always lived at sea level. It has been thought that delirium as a complication in infectious disease at high altitudes is more fatal than at low altitudes, but this is not proved.(3) The outstanding characteristics of the deliriums studied are: Push of irrational talk, vocal and general motor restlessness, visual hallucinations (rather than auditory) of moving objects, animals or people, peculiar feelings, unreality feelings, delusions that are transitory and annoying, blind groping, sleepiness, defective perception, and distorted awareness of environment.(4) The most common diseases associated with the group of deliriums studied are typhoid fever, pneumonia, and influenza. There is no evidence from this study that there are deliriums peculiar to these diseases.(5) The character of delirium, whatever its exciting cause, is largely determined by the personality of the individual, and as such, shows a great variety of reactions.For assistance in this study the writer is indebted to the Social Service Department of the Colorado Psychopathic Hospital, especially to Miss Lena Pecover, and to Surgeon Lawrence Kolb, of the United States Public Health Service.