Background: Genital Chlamydia trachomatis is common among young, sexually active people and is the leading cause of pelvic inflammatory disease. Infections are most often asymptomatic but have potential long-term consequences for female reproductive health. Ectopic pregnancy is one of the most severe complications of pelvic inflammatory disease associated with genital chlamydia infection in the general female population. However, recent studies show divergent results concerning the risk of ectopic pregnancy following Chlamydia trachomatis infection. Objective: To determine the association between evidence of prior Chlamydia trachomatis infection and the risk of ectopic pregnancy. Methods: This was a case-control study from the Obstetrics and Gynaecology departments of two tertiary level health care facilities in Benin City. Ninety eight women with ectopic pregnancy and another 98 women with uncomplicated intrauterine pregnancy matched for age, were interviewed using a semi-structured questionnaire and evaluated for serological evidence of prior Chlamydia trachomatis infection.