The evidence for M genitalium as a sexually acquired infection in women is strong, and the organism has been associated with cervicitis and urethritis. In vitro evidence supports the concept that M genitalium causes inflammation in the fallopian tube epithelium, and animal studies have demonstrated the potential for infection to spread from the lower to the upper genital tract. Serologic data in humans who have PID are somewhat conflicting, but studies in infertile women suggest a link between M genitalium and tubal damage. The organism has also been isolated in the endometrium and fallopian tubes of women who have PID. The evidence is therefore accumulating that M genitalium is a cause of PID, and the assessment of reliable tests to further investigate the importance of this organism and its relevance in designing future treatment strategies is urgently needed.