This article is the presentation of the main phobia data from the Epidemiologic Catchment Area (ECA) program, with a sample size of n = 18.571. Work on this article was initiated in 1981 at the beginning of the ECA study, but publication has been delayed a decade. Phobias are determined from information from the Diagnostic Interview Schedule (DIS), classified according to DSM III. Phobias are found to be the most common psychiatric disorder in the community, more common than major depression or alcohol abuse or dependence in the month prior to interview. The one month prevalence is between 4.0 and 11.1%, with the estimated prevalence in the United States being 6.2%. There were nine community surveys of the prevalence of phobia that pre-dated the ECA studies, which found a wide range of prevalence rates from 1.2% to 26.1%. By far the strongest risk factor associated with phobias is the presence of another psychiatric disorder. Prevalence rates of simple phobia and agoraphobia are found in the ECA studies to be significantly higher in women; social phobia, which is less prevalent, has no significant sex difference. The prevalence rates are higher in younger age groups, and in those with low socioeconomic status (SES). The onset of phobias occurs primarily in the childhood or teenage years, and they tend to be chronic conditions. Less than a quarter of phobics receive treatment.