Abstract The literature on loneliness is reviewed in regard to prevalence, demographics, its relationship to psychiatric disorders, and physical disease. Loneliness was found to be a problem for a significant portion of the population, reported more in the young and in women with the exception of older unmarried men. Studies which examine the relationship between loneliness, depression, alcoholism, child abuse, and bereavement are discussed. Studies of the relationship of loneliness with other psychiatric disorders are lacking. There are data relating loneliness to physical disease and possible mechanisms for this relationship are reviewed.