The prevalence and correlates of illness worry in the general population were investigated in a representative sample. The authors screened residents of the United States by telephone, and more detailed interviews were conducted with 123 respondents who reported at least 1 month of worry about serious illness in the past 12 months and an equal number of randomly selected persons without such worry. Data on demographic characteristics, medical and psychiatric conditions, functional impairment, and health care utilization were collected. At least 1 month of worry was endorsed by 13.1% of the screened population. Correlates of worry included a cluster of psychiatric conditions (major depressive episode, panic attacks, and generalized anxiety disorder) and three clusters of physical conditions (heart disease, cancer, and other diseases). Worry about serious illness was associated with functional impairment and health care utilization.