Over 20,000 consecutively enrolled HIV-1 positive patients from over 100 clinical centres in 35 European countries, Israel and Argentina - one quarter from the eastern region - are currently enrolled in EuroSIDA. New cohorts of patients are normally enrolled every 2-3 years to ensure all regions of Europe where the epidemic is prevalent are represented so the study will give timely information on the clinical presentation and outcome of European HIV-1 positive patients. In 2012, 2500 additional patients were enrolled into EuroSIDA cohort IX. To be at the forefront of investigating the benefits and adverse effects of new HCV treatment in co-infected patients, the next EuroSIDA cohort (cohort X) to be enrolled in 2014, will exclusively consist of 5000 HIV-1 patients positive for antibodies against HCV.