Background: Because of the favourable safety and tolerability profiles of atazanavir (ATV) and raltegravir (RAL), attention has recently turned to the use of dual ATV plus RAL therapy as a nucleoside reverse transcriptase inhibitor- sparing treatment strategy in highly antiretroviral treatment (ART)-experienced HIV-infected patients. Methods: A retrospective observational study was carried out to assess the maintenance of viral suppression and ART tolerability in 20 highly ART-experienced patients with viral suppression, who had been switched to RAL and unboosted ATV dual therapy, using data collected during standard-of-care visits. Results: At 6, 12 and 18 months, viral load was maintained at <400 HIV RNA copies/ml, with only one participant recording a detectable viral load (150 copies/ml) at the 6-month time point. Stable CD4 + T-cell counts were maintained throughout the study period. Five participants changed regimen during the 18-month follow-up, with the median time to switch being 9 months (range 2-12). In three cases, patients were changed from dual therapy because of adverse events while on the regimen. These included increased fatigue (two patients), persistently increased bilirubin (one patient) and gastrointestinal side effects (one patient). Two additional patients changed therapy: one patient added lamivudine and one ceased ATV to pre-empt a potential drug-drug interaction. All five patients who switched from ATV/RAL before 12 months follow-up maintained viral suppression, implying no disadvantage from switching to dual therapy. Conclusions: Dual therapy with ATV plus RAL maintained viral suppression in this small group of highly ART-experienced patients. Further investigation of this novel dual therapy regimen is warranted.