This is an observational, non-comparative, multicenter, open-label study. Participants will be treated with Raltegravir according to standard clinical practice, and monitored over a total period of 96 weeks. In an extension to the study (Amendment 1), a new cohort of aging participants (≥ 50 years) will be recruited and monitored over a total period of 48 weeks. Participants who stop taking Raltegravir before the end of the 96-week period or 48-week period, respectively, will be followed up for 3 months after discontinuing the drug. The primary objective is to determine the proportion of participants with a human immunodeficiency virus (HIV)-1 viral load < 50 copies/mL after 48 weeks of treatment with Raltegravir.