BACKGROUND: In Italy, out of 60 millions of inhabitants, 3000 (2700-4000) new HIV infections are estimated each year. As combined antiretroviral therapy (ART) prolongs life for HIV sufferers, the prevalence of HIV-infection is likely to increase over time. Few studies have assessed factors associated with being HIV positive in people accessing public outpatient clinics and, in particular, the influence of socio-economic circumstances on HIV prevalence. This study aims to evaluate the association between subjects' serostatus and socio-economic determinants measured at the individual and neighbourhood levels. METHODS: Data from a large anonymous survey performed in 2012-2014 on more than 10 000 individuals 18-59 years old who underwent 21 public ambulatories in Rome were analysed. Subjects' socio-demographic characteristics, sexual orientation, number of sexual partners, HIV risk behaviour and HIV testing uptake were collected by a self-administered questionnaire. Level of area deprivation was measured at the postal code level by the index of social disadvantage (ISD). Multilevel Poisson regressions were carried out to take heterogeneity between clusters (post code and clinics) into account. RESULTS: Self-reported HIV-prevalence was 2.0% among subjects ever been tested (13.7% for the homosexual/lesbians 7.0% for the bisexual and 1.3% for the heterosexual). About 1% of subjects self-identified as low risk was HIV infected. This prevalence increased up to 2% in the age group 18-34 and up to 5% in the non-heterosexuals (i.e. self- identified homosexuals/lesbians and bisexuals). At the individual level, HIV-prevalence decreased linearly from lowest to highest levels of education. Living in a deprived neighbourhood was not associated with HIV-infection. CONCLUSIONS: Our study confirms high HIV prevalences among homosexuals/lesbians. Some infections occur in subjects who do not report high risk behaviours for HIV transmission.