Introduction: Early diagnosis is a crucial tool for containing the human immunodeficiency virus and other sexually transmitted infections, particularly in key populations such as sex workers. Despite its relevance, there is a gap considering epidemiological studies and interventions aimed at the monitoring and diagnosis of sexually transmitted infections in Portugal. The objectives of this study are: (i) to contribute to a better understanding of the epidemiology of sexually transmitted infections; and (ii) to evaluate the transfer of screening methods from clinical settings to the outreach context in hidden populations such as sex workers.Material and Methods: The screening of sexually transmitted infections (human immunodeficiency virus 1/2, hepatitis B virus, hepatitis C virus, syphilis, chlamydia and gonorrhea) were carried out in a sample of 100 sex workers during the Porto G outreach intervention in the Metropolitan area of Porto, from September 2015 to September 2016.Results: Six reactive cases for human immunodeficiency virus were identified, five of syphilis, eight of chlamydia and two of gonorrhea. No positive results were detected for hepatitis B virus and hepatitis C virus. The results were discussed considering the risk gradient and sexually transmitted infections vulnerability in the different sex workers’ subgroups.Discussion: The results of this study corroborate the need to promote comprehensive responses to populations most affected by the human immunodeficiency virus and other sexually transmitted infections, such as sex workers. Also, in this group, men who have sex with men and trans women have a higher prevalence than cis women. Intervention strategies should be informed by rigorous epidemiological studies.Conclusion: The adaptation of the screening methodology performed in a clinical setting to the proximity context has shown to be an innovative response in Portugal, especially in sentinel populations.