Sexually transmitted infections caused by Chlamydia trachomatis (Ct) and Mycoplasma genitalium (Mg) have significant implications both at the individual and societal levels. Our study evaluated various co-factors associations with persistent serum IgG-antibodies to Ct and Mg. 329 pregnant women and 135 men from the Finnish Family HPV study were analysed for serum IgG-antibodies of pGP3 for Ct and MgPa and rMgPa for Mg using multiplex serology. Seropersistence to both Ct and Mg was more common in women (30.4% and 13.3%) than in men (17.4% and 5.3%). The number of lifetime sexual partners above 10, practice of anal sex, and history of diagnosed Ct were associated with seropersistence to Ct in women, adjusted ORs 5.6 (95%CI 1.39-22.29), 15.3 (95%CI 1.18-197.12) and 18.0 (95%CI 5.59-57.92), respectively. The increasing number of partners before the age f 20 was the main risk factor for seropersistence among women with Mg, adjusted OR range from 5.0 to 12.3 (95%CI range 1.17-100.90) and in men only with 6 to 10 partners for Ct, adjusted OR 12.6 (95%CI 1.55-102.49). To conclude, persistent Ct antibodies were associated with various sexual activities, and Mg seropositivity was mainly associated with increased sexual activity in early 34 adulthood.