Abstract: LIU Pai, CAO Ning-xiao, SHI Mei-qin, ZHANG Jin-ping, JIANG Juan, SUN Jian-fang. Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing 210042, China Corresponding authors: JIANG Juan, Email: drjjiang@vip.163.com; SUN Jian-fang, Email: fangmin5758@aliyun.com 【Abstract】 Objective To estimate the prevalence of sexually transmitted diseases（STDs） among men who have sex with men（MSM） in some cities of Jiangsu province. Methods A cross-sectional questionnaire survey was carried out among MSM attending gay bars in some cities of Jiangsu province. Participants underwent screening for STDs in accordance with their personal wishes. Urethral swabs, first void urine and blood samples were collected at these survey sites and delivered to the STD research laboratory for testing. Univariate analysis and multivariate logistic regression analysis were performed to assess factors associated with STDs. Results A total of 388 subjects completed the questionnaire and underwent physical examination and STD screening. Of these subjects, 45.6% had only homosexual behavior. Examination of urine or urethral swab specimens showed that the prevalence rate was 1.3％ （5/388）, 9.4％ （36/385）, 17.2％ （66/384） and 28.1％ （109/388） for Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasma genitalium and Ureaplasma urealyticum infection respectively. Serological tests revealed that the positivity rate was 1.0% （4/388） for anti-human immunodeficiency virus （HIV） antibody, 18.8％（73/388） for Treponema pallidum particle agglutination assay （TPPA）, 12.1％（47/388） for rapid plasma reagin （RPR） test, 9.8％ （38/388） for human herpes simplex virus （HSV）-2-IgG, 9.8％ （38/388） for hepatitis B surface antigen, 1.0% （4/388） for anti-hepatitis C virus antibody and 2.1％ （8/388） for anti-hepatitis E virus antibody. Multivariate analysis indicated that Chlamydia trachomatis infection was independently and significantly associated with polymorphonuclear leucocyte （PMNL） counts in urethral swab smears （adjusted odds ratio （AOR）: 5.30, 95% CI: 2.04 － 13.77, P < 0.01）, Mycoplasma genitalium infection was significantly associated with age （AOR: 2.84, 95% CI: 1.17 － 6.87, P < 0.05）, PMNL counts in urethral swab smears （AOR: 2.37, 95% CI: 1.01 － 5.57, P < 0.05） and urethral discomfort in the past three months （AOR: 2.43, 95% CI: 1.18 － 5.02, P < 0.05）, and syphilis （defined as a positive TPPA and RPR test） was associated with age （AOR: 2.46, 95% CI: 1.05 － 5.75, P < 0.05） and seropositivity for anti-HSV-2 antibodies （AOR: 3.70, 95% CI: 1.62－8.44, P < 0.01）. Conclusions There is a high prevalence of STDs among MSM attending gay bars in some cities of Jiangsu province, with Chlamydia trachomatis and Mycoplasma genitalium as the most common pathogens of urethritis. 【Key words】 Homosexuality, male; Sexually transmitted diseases; Sexual behavior