The purpose of this paper is the study of sexually transmitted co-infections in patients with confirmed syphilis and of their contributing factors. According to the established criteria, a total of 55 patients with syphilis were included during the study period. By gender, there were 39 men (71%) and 16 women (29%). We performed the following serological tests on these patients in order to diagnose a sexually transmitted co-infection. The HBsAg was found in 21 cases (38.1%). No HCV antibody was detected in any of the patients. 18 cases (32.7 %) were positive for chronic Chlamydia-specific IgG antibodies. 14 cases (25.4%) had IgA antibodies suggesting a recent Chlamydia infection. All of the patients tested positive for HSV-1 and HSV-2 herpetic antibodies. The study revealed at least one sexually transmitted syphilis co-infection. About 30 % of the patients had at least one co-infection: Hepatitis B virus and Chlamydia. The syphilis infection facilitated the acquisition of the co-infections. Unmarried male patients, with multiple sexual encounters, low educational level and unemployed are the high-risk groups for contracting sexually transmitted diseases and sexually transmitted co-infections.