Pelvic inflammatory disease (PID) is one of the most widespread and debilitating diseases affecting women today. To calculate the economic costs of PID and PID-associated ectopic pregnancy and infertility in the United States, we analyzed data from local hospitals and from several state and national sources. Direct and indirect costs were computed. We found that the total cost of PID and PID-associated ectopic pregnancy and infertility exceeded +2.6 billion in 1984. By 1990, the estimated cost of PID and its sequelae will total +3.50 billion per year, if the annual medical care inflation is 5% and the incidence of PID remains constant during this six-year period. These estimated costs of PID and its associated sequelae emphasize the urgent need for effective programs to prevent PID.