Background: Sexually Transmitted Infections (STI) are a public health issue, which should be promptly diagnosed and treated. Objectives: The objectives of this study were to characterized Chlamydia trachomatis and Neisseria gonorrhoeae infections, namely co-infections between the two and with other STI, and associated demographic factors in population groups volunteering for screening. Methods: C. trachomatis and N. gonorrhoeae infections were diagnosed through a multiplex Real-Time PCR. The presence of N. gonorrhoeae DNA was confirmed by RFLP technique. The presence of antibodies against other STI and of antigens was performed with recommended techniques. Results: The overall prevalence of C. trachomatis and N. gonorrhoeae infection was 3, 4%, and 1, 0%, mostly being asymptomatic in 90% and 83, 3%, respectively. Syphilis, hepatitis C, hepatitis B and HIV were diagnosed respectively in 2, 7%, 5, 1%, 4% and 2%. The majority of infected participants were < 25 years old and those with N. gonorrhoeae males, from whom 50% had a co-infection with C. trachomatis. N. gonorrhoeae infection was associated with a diagnosis of gonorrhoea in the past. Most of the people infected had more than one sexual partner in the previous 6 months (73, 7%) and an inconstant condom use (80, 7%). Furthermore, most individuals are not aware of their high risk sexual behaviour. Conclusion: This study suggests that STI sexual health education, decreasing barriers to health care and non-invasive STI screening are essential in this population and in similar ones.