Background: and Purpose Oral nucleos(t)ide analogs (NAs) are the mainstay treatment for chronic hepatitis B (CHB). Myotoxicity is an important extrahepatic effect related to NA treatment. Telbivudine is the NA for CHB that is frequently associated with muscle-related side effects. The risk factors for telbivudine-induced myopathy (TIM) are not yet clear. Methods: This study characterized the clinical, magnetic resonance images (MRI), and pathological features of 12 TIM cases. A group of telbivudine-tolerant (TT) patients with CHB who received regular telbivudine treatment during the same period without the occurrence of myopathy was collected. Demographic and clinical factors were compared between the patients with TIM and the TT controls. Factors independently associated with TIM were identified using logistic regression analysis. Results: The patients with TIM (males/females: 7/5, mean age: 57 years) developed myopathy after using telbivudine for a median period of 19.5 months. Muscle histopathology revealed abnormal proliferation, subsarcolemmal or sarcoplasmic accumulations, and ultrastructural defects of mitochondria. When compared with TT cases, patients with TIM had a lower estimated glomerular filtration rate and were more frequently positive for hepatitis B e antigen (HBeAg). Conclusions Mitochondrial abnormalities are characteristic histopathological features, and impaired renal function and HBeAg positivity are risk factors for TIM. Telbivudine-induced mitochondrial dysfunction and immune activation related to mitochondrial damage and HBeAg serostatus changes may underlie TIM. Constant clinical surveillance of myopathy during telbivudine treatment is needed due to the significant latency of its development. Dose adjustment for impaired renal function does not eliminate the risk of TIM occurrence.