Pelvic inflammatory disease (PID) and its sequelae affect millions of women in the United States at substantial costs. To estimate these total costs annually and to determine payment sources, we analyzed data from local, state, and national sources. Direct costs for PID and PID-associated ectopic pregnancy and infertility were estimated to be $2.7 billion, and indirect costs were estimated to be $1.5 billion, for a total cost of $4.2 billion in 1990. Overall, private insurance covered the largest portion of the direct costs of PID (41%), followed by public payment sources (30%). However, the proportion of payments made by private insurance appears to be decreasing, while that by public payment sources is increasing. In the year 2000, costs associated with PID are projected to approach $10 billion if the current PID incidence persists, with an increasing proportion of this expense burdening public institutions. Prevention of PID is needed both to reduce human suffering and to contain rising costs.