Introduction The Acquired Human Immunodeficiency Syndrome is one of the main public health problems in Brazil and in the world. The HIV epidemic is concentrated in major urban centres, with high prevalence among the vulnerable population, such as those living on the streets. Studies show that in the last two years, the number of people living with HIV and being on antiretroviral therapy increased about one third, reaching 17.0 million people, 2 million more than the 15 million in 2015. The main goal was to estimate the prevalence of HIV in homeless people.

Methods A cross-sectional study, developed at the Specialised Reference Centre for Homeless People (POP Centre), in the city of Teresina-PI, where participants were recruited using the Snowball technique. The data were collected through a form and a fast HIV test, from August to December/2016. This study comply with the ethical requirements, and had a report of the Research Ethics Committee of the Federal University of Piauí with number 1,755,893.

Results HIV prevalence (n=112) was 7.1%. The age ranged from 19 to over 45 years old, and the prevalence was highest at the age of 25 to 35 years old (2.6%). Of the total number of infected individuals, the participants were single (5.3%), brown (4.5%), had at least one child (2.6%), had their first sexual intercourse between 13 and 19 years old (3.5%), have casual partnership (2.6%) and have no monogamous partnership (3.5%). Regarding to the use of condom with the aforementioned partnership, it was reported as sometimes (0.8%) and (5.3%) reported use of illicit drugs.

Conclusion The prevalence of HIV is high in people living on the street with higher incidence in singles, with early sexual activity, not having a monogamous partnership and use of illicit drugs. It is essential to trace cases in this type of population and control the follow-up of detected cases. In addition, guidance on preventive measures.