A working group of the European AIDS Clinical Society (EACS) have developed these guidelines for European clinicians to help them in the treatment of adults with HIV infection. This third version of the guidelines includes, as new topics, the assessment of patients at initial and subsequent clinic visits as well as post-exposure prophylaxis. A revision of the 2005 guidelines based on current data includes changes in the sections on primary HIV infection, when to initiate therapy, which drug combinations are preferred as initial combination regimens for antiretroviral-naïve patients, how to manage virological failure and the treatment of HIV during pregnancy. In Europe, there is a wide range of clinical practices in antiretroviral therapy depending on various factors such as drug registration, national policies, local availability, reimbursement and access to treatment. These can vary greatly from one country to another, especially in Central and Eastern parts of Europe. These guidelines are intended to help clinicians achieve the best care for their patients. In some countries, particularly where the quality of and access to care are not optimal, these guidelines should help AIDS societies and physicians or patient group organizations to negotiate with their national health authorities with a view to implementing what should be the standard of care for HIV-infected patients all over Europe.