Chlamydia trachomatis has emerged as the most common sexually transmitted bacterial pathogen in the United States and is now recognized to cause substantial morbidity. To determine the economic consequences of chlamydial infections in the United States, we analyzed data from local, state, and national sources. We estimate that C trachomatis infections cost Americans over $1.4 billion per year in direct and indirect costs. Chlamydial infections in women account for 79% of this cost, although men and infants are also affected. Three fourths of the total cost is due to sequelae of untreated, uncomplicated infections. If the current rate of chlamydial infection persists, the projected annual costs will exceed $2.18 billion by 1990. Reducing the incidence of personal suffering and heavy economic burden imposed by C trachomatis infections requires establishment and maintenance of effective prevention/control programs.