Our goal was to determine the prevalence of, and risk factors associated with, syphilis in HIV-infected patients who attend an AIDS outpatient clinic in Vitoria, Brazil. We conducted a cross-sectional study—including interviews for demographic, behavioral, and clinical characteristics—and blood collection (venipuncture and fingerstick) for VDRL and treponemal tests (rapid test) in a total of 438 patients. The mean age was 43.0 years (SD = 11), and mean years of school was 8.1 (SD = 4.2). The prevalence of syphilis was 5.3 % (95 % CI 3.3–7.3). The treponemal test was positive in 18.9 % of participants. In multivariate analysis, prevalent syphilis infection was independently associated with male gender (AOR 4.6, 95 % CI 1.1–20.0), a history of male–male sex (AOR 1.8, 95 % CI 1.6–4.1), current use of antiretroviral therapy (AOR 5.5, 95 % CI 1.7–16.7), and history of treated syphilis infection (AOR 5.5, 95 % CI 2.0–15.8). Syphilis prevalence was high in patients living with HIV/AIDS who attend an AIDS clinic; therefore, routine sexually transmitted infections counseling and screening should be included in their care.