PID is a major medical, economic, and public health problem in the United States. It is the most common serious complication of sexually transmitted diseases among young women. Of great concern is the increasing incidence of adverse reproductive consequences that are thought to be directly related to PID. The most common and important sequelae are tubal factor infertility and ectopic pregnancy. Retrospective serologic evidence has been generated by many studies implicating previous chlamydial infection as a major cause of tubal factor infertility and probably of ectopic pregnancy. Treatment of PID must include regimens effective against a broad range of pathogens, including N. gonorrhoeae and C. trachomatis.