A 22 year old woman in a new sexual relationship presented to her general practitioner with slightly painful intermenstrual bleeding for 10 days. She had pelvic tenderness but no cervical excitation on bimanual examination. The doctor suspected that the bleeding was a side effect of the oral contraceptive pill, started three months earlier. However, as he was unable to rule out pelvic inflammatory disease (PID), endocervical swab samples were taken to test for the sexually transmitted infections caused by Neisseria gonorrhoeae and Chlamydia trachomatis , and broad spectrum antibiotics prescribed, after which the symptoms resolved. The swab sample confirmed the presence of C trachomatis . PID is due to infection of the upper female genital tract resulting in a wide range of pelvic pathology, from mild endometritis to pelvic peritonitis. Causative organisms are either sexually transmitted (such as C trachomatis , N gonorrhoeae , Mycoplasma genitalium ) or endogenous vaginal organisms (for example, Bacteroides species) that ascend into the pelvic area from the lower genital tract through the cervix. #### How common is PID? PID may present with classic symptoms and signs or with mild and subtle symptoms that may be easy to miss, according to a review of the evidence in national guidelines written by the British Association for Sexual Health and HIV.2 The best recent data on easily missed PID come from a retrospective audit in a walk-in centre for sexual health. This showed significantly different rates for the diagnosis of PID among 23 doctors, compared with similar rates …