'Background. The HIV epidemic is a major public health issue in Europe. Over the last decade significant changes in the epidemic have taken place with a increasing proportion of HIV infections being in migrants and women. In turn, these groups might not fully benefit from life-saving antiretroviral treatments (ART), because of barriers to HIV testing and to ART. To date no study with sufficient sample size has explored the role of socio-economic determinants in heath of HIV infected patients in Europe. The role of contextual factors in the health of HIV patients, such as ethnic density, and lower area income level, have not been studied. Objective. We aim to study the socio-economic determinants of inequalities in HIV diagnosis, disease progression, and treatment initiation in Western Europe. Moreover, we will explore the extent to which the variability of HIV prognosis is attributable to either individual (gender, ethnicity, social class) or contextual factors (income area, ethnic density). We will use the routinely collected data of HIV infected patients that will be merged by the newly established EuroCoord collaboration. Methods. The routinely collected database from the newly established EuroCoord collaboration provides information on socio-economic determinants on 250,000 HIV infected individuals from various EU countries. HIV disease progression will be defined as rate of CD4 decline or time to AIDS or death. Marginal structural models to account for time varying confounding will be used to explore differences by socio-economic groups of the effect of ART on the risk of AIDS and mortality. Multilevel and latent variable models will be used to explore the role of contextual factors on HIV progression. Public health implications. This research will help EU health care planners to identify and target groups of HIV infected individuals likely to face barriers to HIV testing and ART and thus prevent HIV-related mortality in more vulnerable populations.'