Oculo-genital chlamydia caused by Chlamydia trachomatis is the most frequent sexually transmitted infection. The number of laboratory verified cases increases steadily in Denmark. This is due to an increased testing activity but also increased positivity rates. Men show substantially lower test rates than women albeit higher positivity rates and seem to constitute an important reservoir for a continued high prevalence of chlamydia. Screening and treatment of especially younger sexually active individuals, not at least men, is vital in controlling the disease.