OBJECTIVES: To estimate the budgetary impact of adding dolutegravir to the Ontario Drug Benefit Formulary (ODBF) for a three-year period for the treatment of HIV infection in adults and children (≥12 years of age). METHODS: Three discrete populations were considered: treatment-naïve (TN) patients staying on their first line, TN switchers (assumed switches within the first 6 months of antiretroviral therapy (ART) initiation) and treatment-experienced (TE) patients. Epidemiology data were obtained from published sources. Ontario-specific data and analysis from the IMS Brogan Database were used to estimate the proportion of patients who were treated and covered by the ODBF, proportions of patients remaining on their first regimen after ART initiation over time, comparators and historical market share data. ART drug costs were calculated based on the dosage of each regimen component from the respective product monographs and unit costs from the ODBF. The budget impact was calculated for the whole HIV population and separately for each population. Sensitivity analyses were conducted on five key input parameters. RESULTS: Out of the 12 comparators, dolutegravir-containing regimens were assumed to take market shares from 6 regimens: Atripla, Truvada⁄Prezista⁄Norvir, Truvada⁄Isentress, Truvada⁄Reyataz⁄Norvir, Kivexa⁄Isentress and Stribild. Adding dolutegravir to the list of reimbursed ARTs on the ODBF will result in incremental savings in each of the three years following the listing date of $2,717,585, $5,181,704, and $8,040,076 for a total savings of $15,939,365. The analysis was somewhat sensitive to assumptions made regarding HIV incidence and prevalence and the proportion treated with drug benefits. Based on the accuracy of the assumptions made in this analysis, the total savings to the budget over a three-year period may range between $12,751,492 and $19,127,238. CONCLUSIONS: The addition of adding dolutegravir to the ODBF will result in a significant net savings through the displacement of more expensive regimens in Ontario.