Two studies are reported that examine the relevance of Erikson's (1959) developmental theory to understanding insomnia. Study 1 investigates the relationship between sleep disturbances in the elderly and the resolution of the psychosocial crisis of "ego integrity versus despair." Questionnaires designed to assess relevant background information, resolution of the psychosocial crisis of ego integrity versus despair, and sleep behavior were administered to 122 institutionalized and noninstitutionalized elderly persons. Multivariate analyses provide strong support for the hypothesis that ineffective resolution of the psychosocial crisis of old age, that is, high levels of measured "despair," is related to sleep disturbances in the elderly. Study 2, designed to provide supportive validation of the relevance of Erikson's developmental theory to understanding insomnia, examines the relationship between resolution of the "identity versus role confusion" psychosocial crisis and sleep disturbances in 66 college students. Analyses of the students' responses to questionnaires assessing these variables provide strong support for the hypothesized relationship between insomnia and incomplete resolution of the adolescent crisis. Implications of the results in terms of understanding both sleep disturbances at other developmental stages and other forms of psychological disfunction are discussed.Interest in the relationships among psychological adjustment, personality characteristics, and sleep has existed for some time.