Chlamydia trachomatis has for long been considered to be a major contributor to tubal infertility. However, the scientific evidence based on human clinical research is weak. C. trachomatis is associated with pelvic inflammatory disease, and pelvic inflammatory disease is associated with tubal infertility. But no interventional trial nor well-conducted study or large cohort study has assessed the risk of infertility given an undiagnosed or untreated genital chlamydial infection. We suggest that the many well established registers in Denmark serve to further elucidate the evidence.