Erythrodermic psoriasis is a severe type of psoriasis associated with systemic symptoms. Immunobiological medications are prescribed for certain patients with severe forms of psoriasis, however, these drugs increase the risk of reactivation of viral or other infectious diseases. We report a 56-years-old man who diagnosed with erythrodermic psoriasis. He had positive serology for the Hepatitis B virus, and treated with acitretin. In this patient, immunomodulating drugs, such as cyclosporine and other biologics, should not be prescribed. The patient markedly improved after treatment without reactivation of viral disease. HBV infection is the most common cause of chronic liver diseases and hepatocellular carcinoma in Korea. The close surveillance of the patients`` HBV status before and during therapy with any immunobiologic agent is recommended. In addition, laboratory tests are fundamental in monitoring liver function for early detection of viral reactivation