The K65R mutation in HIV-1 reverse transcriptase (RT) can be selected by the RT inhibitors tenofovir (TDF), abacavir (ABC), and didanosine (DDI). Recently, in vitro studies have shown that K65R is selected in tissue culture more rapidly with subtypeC than subtypeBviruses. The prevalence of K65R in viruses sequenced at the Tel-Aviv AIDS Center was evaluated. This study analyzed retrospectively sequences from 1999 to 2007 in patients treated with TDF, ABC, and/or DDI and compared rates of mutational prevalence between subtypes. Fisher's exact test was used to determine statistical significance. Forty-four sequences from patients treated with the three above-cited drugs were analyzed. Subtypes A (n=1), CRF01-AE (n=4), CRF02-AG (n=2), B (n=21), C (n=11), D (n=1), F (n=3), and G (n=1) were represented. Seven non-B viruses had the K65R mutation, which was only found in one subtype B virus. Of these seven samples four were subtype C, one was subtype CRF01-AE, and two were subtype CRF02-AG. None of the eight viruses with K65R harbored thymidine analogue mutations. In this study, non-subtype B viruses possessed the K65R mutation at higher incidence than subtype Bviruses. SubtypeCvirusesmaybe especially prone to develop this mutation. Larger studies are needed to confirm these data. Efforts should be intensified to understand better differences in drug resistance between various HIV subtypes.