Aim: To determine if exclusive breastfeeding (EBF) or exclusive formula feeding (EFF) is more cost-effective when the mother is living with HIV and fully virally suppressed. This research was conducted in Canada where mothers living with HIV are currently advised to practice EFF to eliminate the risk of perinatal transmission. Methods: A micro-simulation model was developed to estimate lifetime costs and effectiveness of EBF and EFF, from the Ontario Ministry of Health perspective. Uncertainties around model parameters were evaluated using one-way and probabilistic sensitivity analyses. Results: In comparison to EFF, EBF was the dominant feeding modality (less costly and more effective) yielding cost-savings of $13,812.49 for each additional quality-adjusted life year. Conclusion: Despite the risk of HIV transmission, EBF was more cost-effective than EFF. These findings suggest that a review be undertaken of current infant feeding guidelines for mothers living with HIV in the context of high-income countries.