The wearing of contact lenses has increased dramatically in the past decade; over 4 million people in the United States now use extended-wear soft contact lenses, and 9 million use daily-wear soft contact lenses. Numerous reports have caused concern that the use of soft contact lenses, especially extended-wear lenses, may result in a substantial risk of ulcerative keratitis. To examine this issue, we conducted a prospective study in five New England states to estimate the incidence of ulcerative keratitis among those who use cosmetic extended-wear and daily-wear soft contact lenses. To obtain the numerator for each estimate of incidence, we surveyed all practicing ophthalmologists in the study area to identify all new cases diagnosed over a four-month period. To provide the denominator, we conducted a survey of 4178 households to estimate the number of persons who wore each type of soft contact lens. The annualized incidence of ulcerative keratitis was estimated to be 20.9 per 10,000 persons using extended-wear soft contact lenses for cosmetic purposes and 4.1 per 10,000 persons using daily-wear soft contact lenses for cosmetic purposes (P less than 0.00001).