Most patients with hepatitis B virus (HBV) have no symptoms, and many are unaware of the infection. However, HBV can reactivate with immunosuppression; chemotherapy causes reactivation in 22 % of hepatitis B surface antigen-positive patients. HBV reactivation can be fatal. HBV reactivation can be prevented, provided that HBV is recognized prior to chemotherapy. The objective of this study is to estimate the health and economic effects of HBV screening strategies in patients receiving adjuvant chemotherapy for breast cancer. We developed a state-transition microsimulation model to examine the cost-effectiveness of three HBV screening strategies: (1) "No screening"; (2) "Screen-and-Treat to prevent reactivation" (screen-all) with either lamivudine/tenofovir (LAM/TDF) or entecavir (ETV); and (3) "Screen-and-Treat high-risk only" (screen-HR) and treat with either LAM/TDF or ETV. Model data were obtained from the published literature. We used a payer's perspective, a lifetime horizon, and a 5 % discount rate for the analysis. "Screen-all" would prevent at least 38 severe reactivations per 100,000 persons screened over the lifetime of the cohort. "Screen-all" was associated with an increase of 0.0034-0.0035 QALYs and an additional cost of C$164-C$266 per person, which translated into an incremental cost-effectiveness ratio of C$47,808/QALY-C$76,527/QALY gained compared with "No screening" depending on the antiviral therapy received. "Screen-all" was the most cost-effective strategy, while "Screen-HR" was inferior in all scenarios tested. HBV screening before adjuvant chemotherapy for breast cancer patients would prevent a significant number of reactivations, would likely be moderately cost-effective, and may extend the lives of breast cancer patients.