Mycoplasma genitaliumis a sexually transmitted pathogen that is increasingly identified among women with pelvic inflammatory disease (PID). AlthoughChlamydia trachomatisandNeisseria gonorrhoeaefrequently cause PID, up to 70% of cases have an unidentified etiology. This paper summarizes evidence linkingM. genitaliumto PID and its long-term reproductive sequelae. Several PCR studies have demonstrated thatM. genitaliumis associated with PID, independent of gonococcal and chlamydial infection. Most have been cross-sectional, although one prospective investigation suggested thatM. genitaliumwas associated with over a thirteenfold risk of endometritis. Further, a nested case-control posttermination study demonstrated a sixfold increased risk of PID amongM. genitaliumpositive patients. Whether or notM. genitaliumupper genital tract infection results in long-term reproductive morbidity is unclear, although tubal factor infertility patients have been found to have elevatedM. genitaliumantibodies. Several lines of evidence suggest thatM. genitaliumis likely resistant to many frequently used PID treatment regimens. Correspondingly,M. genitaliumhas been associated with treatment failure following cefoxitin and doxycycline treatment for clinically suspected PID. Collectively, strong evidence suggests thatM. genitaliumis associated with PID. Further study ofM. genitaliumupper genital tract infection diagnosis, treatment and long-term sequelae is warranted.