For cancer patients with chronic hepatitis B virus (HBV) infection, who receive cytotoxic chemotherapy, HBV reactivation is a well-described complication, which may result in varying degrees of liver damage. Several clinical features and the pre-chemotherapy HBV viral load have been suggested to be associated with an increased risk of developing the condition: (1). to assess the clinical and virological factors in a comprehensive manner and thereby identify those that are associated with the development of HBV reactivation; (2). to develop a predictive model to quantify the risk of HBV reactivation. In all, 138 consecutive cancer patients who were HBV carriers and undergoing chemotherapy were studied, of which 128 patients had sera available for real-time PCR HBV DNA measurement. They were followed up throughout their course of chemotherapy and the HBV reactivation rate was determined. The clinical and virological features between those who did and did not develop viral reactivation were compared. These included age, sex, baseline liver function tests, HBeAg status and viral load (HBV DNA) prior to the chemotherapy, and the use of specific cytotoxic agents. In all, 36 (26%) developed HBV reactivation. Multivariate analysis revealed pre-chemotherapy HBV DNA level, the use of steroids and a diagnosis of lymphoma or breast cancer to be significant factors. Based on real-time HBV DNA PCR assay, detectable baseline HBV DNA prior to the administration of cytotoxic chemotherapy, the use of steroids and a diagnosis of lymphoma or breast cancer are predictive factors for the development of HBV reactivation. A predictive model was developed from the current data, based on a logistic regression method.