BACKGROUND: Individuals who had past hepatitis B virus (HBV) infection appeared to clear their serum hepatitis B surface antigen (HBsAg) while producing antibody to the hepatitis B core antigen (HBcAb), which is detectable in their serum. Currently, it is uncertain whether patients with past HBV infection require routine antiviral prophylaxis during chemotherapy, although some cancer agencies recommend its routine use. The objective of the current study was to determine the prevalence of past HBV infection in patients with lymphoma and its relevance in terms of HBVrelated complications. METHODS: The authors reviewed 430 patients with lymphoma from May 2006 to May 2008. RESULTS: Among the 430 patients, 233 had both the HBsAg and HBcAb tests performed, whereas 197 had only the HBsAg test performed. Among those with both tests performed, 34.3% (80 of 233) were HBcAb positive only. Of these 80 patients, 58 had a concomitant HBV DNA level test, which was positive in 3 (5.2%). Of the 67 patients with past and 26 with chronic HBV infection who received chemotherapy, HBV reactivation occurred in 1.5% and 42.3% of patients, respectively (P<.0001). Prophylactic lamivudine was administered in 7 (10.4%) patients with past HBV infection and in 18 (69.2%) with chronic HBV infection. CONCLUSIONS: The low rate of HBV reactivation reported in our study coupled with the high prevalence of past HBV infection in an endemic area suggests that routine usage of antiviral prophylaxis may not be required for all patients with past HBV infection. Close surveillance remains a reasonable and viable option for the majority of patients. Cancer 2010;116:115-21.