This project thesis is about HIV-resistance in the light of the use of pre-exposure prophylaxis (PrEP) in Norway. PrEP is a daily or intermittent hiv-medicine taken by healthy individuals in high risk of HIV-transmission in order to reduce the risk of being infected. PrEP consist of a combination of the two antiretroviral drugs tenofovir and emitricitabine (TDF/FTC). If taken as recommended, PrEP has proven to reduce the risk of HIV-transmission significantly (2,3,4). There has been concerns as to whether the use of PrEP will increase the prevalence of HIV resistant to the drugs used in PrEP, as the same drugs are also used in standard HIV therapy. The benefit of preventing new infections seems to outweigh the low risk of PrEP selecting TDF/FTC resistance. The situation associated with the highest risk for development of drug resistance, is whenever PrEP is given to a person with acute unrecognized HIV infection at an early stage, before the infection can be detected by the HIV test. This has been shown in clinical trials (6). The main question of my thesis is whether the prevalence of HIV resistance against the drugs used in PrEP in Norway has changed after the introduction of PrEP in 2017. My results show that the prevalence of TDF/FTC- resistance was reduced two years after the introduction of PrEP compared to the prevalence in 2012-2016. However, due to short observation period and several limitations of the study, we cannot assume that this reduction can be directly attributed to the introduction of PrEP. Several years of surveillance and research is necessary to determine the future impact of PrEP on HIV drug resistance - whether it will increase, remain unchanged, or decrease.