The goal is to establish serological invasive markers of Chlamydia trachomatis in female prisoners and to analyse the risk factors for the spread of chlamydial infection in prisons in Ukraine. When studying a sample of 103 female prisoners (whose average age is 35.9 years), serological markers of Chlamydia trachomatis (immunoglobulin G) were analysed. Social characteristics of prisoners and risk factors for chlamydia spread have been analysed. Markers of Chlamydia trachomatis (class G immunoglobulins) were detected in serum of 37.8% of female prisoners. In the majority of cases, chlamydia was asymptomatic or in the form of chronic endocervicitis (53.8%), adnexitis (38.5%), and urethritis (17.9%), which was a mixed process with other STIs and HIV (HSV-1 (up to 100%), HSV-2 (30%), Treponema pallidum (26.6%), Ureaplasma urealyticum (6.6%), HBV (26.6%), HCV (33.3%), HIV (30%)). Identified infection risk factors: age over 25 years, HIV, HSV, HCV, HBV, and other STIs, endocervicitis, chronic pelvic pain, urethritis, risky sexual behaviour, drug use, alcoholism, prolonged or repeated confinement, absence of family. The prevalence of Chlamydia trachomatis among female prisoners in Ukraine (37.8%) is 2.5 times higher often and significantly higher (P<0.05) than among women with a predominance of chronic inflammatory diseases of the pelvic organs and significantly higher than in the general population (20.9 per 100,000).