ABSTRACT Background: Sexually Transmitted Infection is still a public health problem globally, because the pattern of the disease almost occurs in all countries until now, especially syphilis. Homosexual behavior, sexual promiscuity, and migration from one place to another can be potential to be transmitted by syphilis. This study aimed to analyze the influence of behavioral factors towards the incidence of syphilis in the work area of the Public Health Centers in Medan, 2019. Subjects and Method: A case control study was conducted in Teladan, Helvetia and Padang Bulan Public health centre. A sample of 80 consisting of 40 cases and 40 control was selected by purposive sampling. The dependent variable was syphilis. The independent variables were HIV status, history of sexually transmitted diseases, previous history of syphilis, history of circumcision, use of condoms, use of drugs, number of sex partners and the average frequency of sex. The data were collected by questionnaire and analyzed by a multiple logistic regression. Results: Variables that influence syphilis are the history of syphilis (OR= 28.52; 95% CI= 7.55 to 107.78; p= 0.0001) and drug use (OR= 15.12; 95% CI= 2.57 to 89.24; p= 0.003). Meanwhile, HIV status (OR = 1.55; 95% CI= 0.41 to 5.87; p= 0.520), use of condoms (OR= 0.2 01; 95% CI= 0.63 to 8.90; p= 0.201) and sexually transmitted diseases (OR= 1.53; 95%CI= 0.23 to 10.18; p= 0.660). The previous history of syphilis was the dominant influence of the incidence of syphilis (OR=28.52; 95% CI= 7.55 to 107.78; p=0.001). Conclusion: Variables that influence syphilis are the history of syphilis (OR= 28.52; 95% CI= 7.55 to 107.78; p= 0.0001) and drug use (OR= 15.12; 95% CI= 2.57 to 89.24; p= 0.003). Meanwhile, HIV status (OR = 1.55; 95% CI= 0.41 to 5.87; p= 0.520), use of condoms (OR= 0.2 01; 95% CI= 0.63 to 8.90; p= 0.201) and sexually transmitted diseases (OR= 1.53; 95%CI= 0.23 to 10.18; p= 0.660). The previous history of syphilis was the dominant influence of the incidence of syphilis (OR=28.52; 95% CI= 7.55 to 107.78; p=0.001). Conclusion: It is recommended that the Health Service of Medan can give inputs for developing health intervention program, including the evaluation of STI intervention programs. The management of Teladan, Helvetia and Padang Bulan Public Health Centers should increase counseling, medication, and prevention programs towards syphilis for the high risk male population. Keywords: Influence, Syphilis, Case Control Correspondence: Vicky Arfeni Warongan, SKM. Fakultas Kesehatan Masyarakat, Universitas Sumatera Utara. Jl. Universitas No.32, Padang Bulan, Kecamatan Medan Baru, Kota Medan, Sumatera Utara 20222. Email: [email protected]. Mobile: 081263197791 DOI: https://doi.org/10.26911/the7thicph.01.22