 Chlamydial infection is a common, sexually transmitted disease which women can have without knowing. Untreated, it can lead to an infection of the womb and fallopian tubes called pelvic inflammatory disease PID, which can cause infertility. There has been only one trial of chlamydia screening and this was in American women in 1992 and used outdated tests. We now need to see if screening using modern tests and self-taken swabs works in a high risk, young, multiethnic female population in the United Kingdom UK. 