BACKGROUND:Little is known about prevalence of drug resistance among HIV-infected Ugandans, a setting with over 15 years of public-sector access to antiretroviral therapy (ART) and where virological monitoring was only recently introduced. SETTING:This study was conducted in the adultsʼ out-patient clinic of the Infectious Diseases Institute, Kampala, Uganda. METHODS:HIV genotyping was performed in ART naïve patients and in treatment experienced patients on ART for ≥ six months with virological failure (≥1000 copies/mL). RESULTS:A total of 152 ART naïve and 2511 ART experienced patients were included. Transmitted drug resistance was detected in 9 (5.9%) patients. After a median time on ART of 4.7 years (interquartile range (IQR)2.5-8.7), 190 patients (7.6%) had virological failure with a median viral load of 4.4 log10 copies/mL (IQR:3.9-4.9). Additionally, 146 patients had a viral load between 51 and 999 copies/ml. Most patients with virological failure (142, 74.7%) were on first-line ART. For 163 (85.8%) ART experienced patients genotype results were available. Relevant drug resistance mutations were observed in 135 (82.8%), of which 103 (63.2%) had resistance to two drug classes, and 11 (6.7%) had resistance to all drug classes available in Uganda. CONCLUSION:The prevalence of transmitted drug resistance was lower than recently reported by the WHO. With 92% of all patients virologically suppressed on ART, the prevalence of virological failure was low when a cut-off of 1000 copies/mL is applied, and is in-line with the third of the 90-90-90 UNAIDS targets. However, most failing patients had developed multi-class drug resistance.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial License 4.0 (CCBY-NC), where it is permissible to download, share, remix, transform, and buildup the work provided it is properly cited. The work cannot be used commercially without permission from the journal.