OBJECTIVES: To evaluate adherence to treatment, healthcare resource use and costs in "single tablet" E/C/F/TDF vs "multi-tablet" regimens using PIs or INIs + dual NRTI backbone (BB). METHODS: Preliminary analysis from an observational retrospective study was performed through the administrative and laboratory databases of two out three Infectious Diseases Departments participating to this study (ASST Valle Olona, Busto Arsizio and IRCCS San Raffaele, Milan). HIV patients were included if they had at least one prescription for an antiretroviral agent between 01/2012 and 02/2015.Follow-up was: 48 weeks; all analyses were stratified according to treatment status (naïve/experienced). Average adherence, healthcare resource use and related costs were analyzed. A multivariate regression model with the covariates:age, sex, treatment experienced, non-adherence, viral load (VL) ≥50 and CD4≤ 200 at baseline was used. RESULTS: CONCLUSIONS: ECFTDF was associated with significantly greater adherence and lower mean annual cost compared to PI+BB. Given the limited number of INI+BB patients, differences observed were not statistically significant and further analysis including patients from the third infectious disease department is needed to confirm these preliminary results.