BACKGROUND: Children and adolescents with HIV have lower treatment success than adults. Suboptimal adherence and resistance to antiretroviral therapy (ART) are known aetiological factors. This preplanned analysis in the GIVE MOVE trial (NCT04233242) describes drug resistance patterns in children and adolescents in Lesotho and Tanzania. MATERIALS AND METHODS: GIVE MOVE randomized children and adolescents (6 months to below 19 years) with recent viraemia whilst taking ART to genotypic resistance testing (GRT)-informed care or usual care. Here, we conducted additional post-hoc GRT on stored samples from both groups and included participants with at least one successful resistance test. We assessed the number of drugs predicted to be active in participants' three-drug ART regimens and resistance-associated mutations. RESULTS: Amongst 137 participants, the majority were female (58%) and lived in Lesotho (77%). At their initial GRT, 69/137 (50%) were receiving protease inhibitor-based, 59/137 (43%) dolutegravir-based and 9/137 (7%) efavirenz-based ART. At that time, 80/137 (58%) participants had three, whilst 8/137 (6%) had two, 36/137 (26%) had one and 13/137 (9%) had no drugs predicted to be active in their regimens. Seventeen (12%) participants had resistance against their ART core agent, including one with high-level dolutegravir resistance.Across 312 detected resistance-associated mutations (222 major, 90 accessory), 146 conferred resistance to non-nucleoside reverse transcriptase inhibitors, 127 to nucleoside reverse transcriptase inhibitors, 28 to protease inhibitors and 11 to integrase strand transfer inhibitors. CONCLUSION: Given that more than half had an ART regimen predicted to be fully active, most viraemia in children and adolescents could not be explained by resistance.Registration: The GIVE MOVE trial was registered on Clinicaltrials.gov NCT04233242.