Background: The seroprevalence of Hepatitis B virus (HBV) infection among Canadian was 0.4%, and 1.6% among immigrants. Most infected individuals have clinically silent disease. Cytotoxic chemotherapy causes reactivation in 30% of the HBV infected patients. This can be severe and fatal, may also lead to interruption of chemotherapy. HBV screening before adjuvant chemotherapy (ADJ) for breast cancer (BC) seems to be a plausible strategy. Our objective is to estimate the health and economic effects of HBV screening strategies. Methods: We developed a state transition microsimulation model to examine the cost effectiveness of 3 strategies for 55 year old BC patients undergoing ADJ: (1) No screen; (2) Screen Imm: Screen immigrant only and treat; (3) Screen all: Screen all and treat; with antiviral therapies. In the model, health states were constructed to reflect the natural history of BC and HBV. Model data were obtained from published literature. We used a payer perspective, a lifetime time horizon, and used a 5% discount rate. Results: Screen all would prevent 38 severe reactivations (SR), 9 deaths from reactivation (DR), 21 chemotherapy interruptions (CI), 32 decompensated cirrhosis (DC), 38 HCCs, and 56 HBV deaths per 100,000 persons screened over the lifetime of the cohort. Screen Imm would prevent 29 SR, 7 DR, 16 CI, 23 DC, 27 HCCs, and 41 HBV deaths. Screen all was associated with an increase of at least 0.0034 quality adjusted life years (QALY) and cost C$164 more per person, translating to an incremental cost effectiveness ratio (ICER) of C$47,808-76,527/QALY gained compared with No screen, depends on different antiviral therapies. Screen all was the most cost effective, while Screen Imm was ruled out due to extended dominance (ED) by No Screen and Screen all. Conclusions: HBV screening before ADJ for BC patients would prevent a significant number of reactivations, and is likely be cost effective.