Introduction:The implementation of the rapid test (RT) for syphilis increases access of vulnerable populations to early diagnosis and treatment, impacting the outcomes of infection. We aimed to assess the prevalence of and factors associated with syphilis in a Center for Testing and Counseling (CTC). Methods: We conducted a cross-sectional study at a Reference Center for sexually transmitted disease (STD) and acquired immune deficiency syndrome in Londrina, Northern Paraná State, Southern Brazil. Data regarding the 5,509 individuals who underwent RT from June 2012 to December 2014 were collected from patient records and the CTC Information System and served as the basis to check associations of syphilis cases (346) and cases without syphilis (5,163). Nine patients' records were not found. OpenEpi was used to perform a prevalence analysis and determine odds ratios to assess the associations between sociodemographic and behavioral variables (independent variables) and cases of syphilis (dependent variable). An alpha value <0.05 was considered statistically significant. Results: The prevalence of syphilis was 6.3%; higher in males (7.5%) than in females (4.3%, p <0.001). Syphilis was associated with an age of 25-34 years, little education, and single marital status. The main associated behavioral factors were men who have sex with men, drug users, STD patients, and those presenting with an STD in the last year. The use of alcohol, marijuana, cocaine, and crack was significantly associated with syphilis. Conclusions: Strategies for prevention and control of syphilis should be intensified, especially in populations identified as most vulnerable.