Background/Aims: Hepatitis B reactivation (HBVR) is an important risk of treatment with tumor necrosis factor inhibitors (anti-TNF). While antiviral prophylaxis is recommended before treatment in hepatitis B surface antigen (HBsAg) positive patients, there is no clear approach for the follow-up or prophylactic treatment of patients with past hepatitis B virus (HBV) infection. This study aimed to evaluate patients with past HBV infection treated with anti-TNF for HBVR and/or HBVR-associated biochemical breakthrough.Materials and Methods: Patients who received anti-TNF therapy and had past HBV infection (HBsAg negative, anti-HBc IgG positive, anti-HBs negative or positive) were screened and evaluated at 3-month intervals for viral and biochemical breakthrough according to a liver function test (ALT) and HBV DNA level.Results: A total of 653 patients who received anti-TNF therapy were screened. Ninety of these patients had past HBV infection and had not received antiviral prophylaxis. Anti-HBs positivity and isolated anti-HBc IgG positivity were seen in 87.7% (n: 79) and 12.2% (n: 11) of these patients, respectively. No HBVR was seen in 20% (n: 18) of patients who were followed up regularly, and no HBVR-associated biochemical breakthrough was found in patients who were not followed up regularly in terms of HBV DNA level (80%, n: 72) during the follow-up period (26±16 months).Conclusion: The use of anti-TNF in patients with past HBV infection has a low risk for HBVR. A follow-up for the ALT and HBV DNA levels at 3-month intervals may be more reasonable than administering antiviral prophylaxis to all patients.