Cross-sectional, single-site, observational Enrolment period: May 1st - July 31st 2015 Patients: All HIV-infected adults above the age of 18 years that have been on a stable first- or second-line ART regimen ≥6 months presenting to the Infectious Diseases Institute (IDI) during the study period and are able to give written informed consent will be enrolled. The goal is to perform viral load testing in 2750 patients on ART. Presuming a detectable viral load in 10%, resistance testing would then be performed in 250 patients on ART. Treatment naive HIV-infected patients above the age of 18 years presenting to the IDI during the study period will be offered resistance testing. The goal is to perform resistance testing in 250 ART naive patients.