OBJECTIVES: Once-daily STRs have become an increasingly popular choice for both newly initiating and treatment experienced patients to improve patient adherence and achieve optimal outcomes. This study examines how STR prescribing trends have evolved in key EU countries (France, Germany, Italy, Spain and the UK) and provides insight into physician motivation to switch from conventional anti-retroviral (ARVs) regimen dosing to STRs. METHODS: Multi-wave retrospective medical chart reviews of HIV patients have been conducted in big-5-EU since 2005 to study patients initiating or switching ARVs during each quarter (Q) of the year. Physicians were recruited from a large panel to be geographically representative; they abstracted patient demographic, disease, and treatment data for next few consecutive HIV patients they encountered within a defined time period. This analysis focuses on STR prescribing trends between 1Q2009 and 4Q2014. RESULTS: Over 200 physicians abstracted 3132 and 3045 patient charts in 1Q2009 and 4Q2014 respectively. STR use increased in EU from 17% (France:0.5%, Germany:12%, Italy:16%, Spain:29%, UK:29%) in 1Q2009 to 51% in 4Q2014 (France:50%, Germany:67%, Italy:41%, Spain:51%, UK:46%). The top reason for switching from conventional ARV dosing to an STR across big-5 EU in 1Q2009 was simplification (72%), followed by tolerability (14%), and patient decision (12%). Importance of tolerability (19%) increased over the past 5 years in the decision to switch, while simplification (64%) decreased; patient decision increased slightly (18%). CONCLUSIONS: STR adoption in the big-5 EU countries studied increased rapidly, with Germany and France having the largest increases from 1Q2009 to 4Q2014. There was a marked change in impetus to switch to STRs from simplification alone to an increasing focus on tolerability. These observed trends may emphasize the importance HIV providers give towards maintaining HIV patients on a simple and yet tolerable regimen to achieve optimal adherence and clinical outcomes over the longer term.