Objective: The aim of the current study is to assess the prevalence of hepatitis B and the risk of hepatitis reactivation in carriers of hepatitis B virus (HBV) cancer patients who underwent chemotherapy for gynecologic and/or breast cancers in a single institution, during a period of five years, and to identify a relationship to some particular chemotherapy regimen, more prone to lead to reactivation. Material and methods: We conducted a retrospective chart review on all consecutive oncological patients treated for a gynecologic and/or breast cancers who presented for the first time to the Gynecologic Oncology Department of Filantropia Hospital, Bucharest, Romania, between January 2016 and December 2020. Results: A total of 1 895 patients diagnosed with ovarian, cervical, endometrial or breast cancers were admitted to hospital for systemic therapy during the mentioned period. Among these, only four patients (two patients with breast cancers, one cervical cancer and one endometrial carcinoma) were chronic carriers of HBV surface antigen (HBsAg positive). Patients received a variety of chemotherapeutic regimens including corticosteroids, gemcitabine, cisplatin, carboplatin, taxanes and anthracyclines. We report one reactivation that occurred in one occult carrier of hepatitis B virus diagnosed with breast cancer (HBsAg negative, hepatitis B core antibody positive - HBcAb), initially excluded from this study, as being screened negative for HBV, treated with taxanes-based chemotherapy and corticosteroids. Conclusion: HBV reactivation had a low incidence in our population of patients diagnosed with gynecologic or breast cancer who received systemic chemotherapy. The HBV reactivation risk was positively correlated with breast cancer and to taxanes-based regimens and glucocorticoids. Further studies to identify additional risk factors of HBV infection reactivation in gynecologic oncology patients and possible risk reducing measures are warranted.