BACKGROUND : Twenty percent of patients infected with hepatitis B virus (HBV) develop extrahepatic manifestations with HBV detected in the lymph nodes, spleen, bone marrow, kidneys, and skin. HBV infection has been associated with some autoimmune disorders. Dermatomyositis (DM) is an idiopathic inflammatory myopathy, which involves a viral infection, and DM has been identified in patients infected with HBV, but there is no direct histological evidence for an association between HBV and DM. METHODS : We describe a familial HBV-infected patient admitted with liver function abnormality, rashes, a movement disorder, and an elevated level of creatine kinase (CK). A computed tomography scan of the lung showed pulmonary fibrosis, and a liver biopsy identified nodular cirrhosis. An electromyogram revealed myogenic damage, and a muscle biopsy showed nuclear migration in local sarcolemma and infiltration of chronic inflammatory cells. Immunohistochemical staining showed negative results for HBsAg and HBcAg. Fluorescence in situ hybridization showed a negative result for HBV DNA. The patient was diagnosed with HBV-related liver cirrhosis complicated with DM and was treated with methylprednisolone, mycophenolate mofetil, and lamivudine. Eight months later, the patient was readmitted for anorexia and fatigue. The blood examination showed elevated levels of aminotransferases and HBV DNA, however, the CK level was within the normal range. The patient developed a virological breakthrough and lamivudine was replaced with tenofovir. CONCLUSIONS : DM in chronic HBV-infected patients does not always associate with HBV. Antiviral and immunosuppressive drugs should be taken into consideration.