Few data are available regarding the prevalence of sexually transmitted infections (STI), including HIV-1 infection, and risk behaviors of transgender individuals. Previous reports indicate that this community has a high prevalence of HIV and STIs. Our objective was to compare the prevalence of HIV-1 infection, STI and risk behaviors of transgender people versus non transgender people. We used a cross sectional design study. Patients who received services at our testing site between November 2002 and April 2006, and provided written informed consent, were included in the analysis. Socio-demographic data, sexual behaviour, recreational drug use, condom use, concurrent or previous STI and HIV-1 infection diagnosis and partner serologic status, were collected. We used descriptive statistics and chi 2 for comparisons of proportions. In the period of the study, 105 transgender individuals were identified in a population of 4118 patients tested. The prevalence of HIV infection in the transgender group was 27.6% (29/105), while in the non transgender group was 6.2% (247/4013) p:0.0000. Low level of formal instruction, alcohol consumption, drug abuse, previous history of STI and sex work (100% transgenders and 2.3% of non-transgenders) were significantly more frequent in the transgender. The referred correct use of condom was similar in both groups. The prevalence of syphilis was 42.3% in transgender group and 18.1% in non-transgender individuals. These data show that this population has a very high prevalence of HIV-1 and STI. This information could be instrumental to design targets for intensive HIV prevention strategies in this particular high risk population.