A sudden death due to hemothorax caused by spontaneous rupture of a congenital pulmonary arteriovenous malformation (AVM) is reported. A 44-year-old woman died unexpectedly with chest pain and dyspnea. The post-mortem examination revealed a massive right-sided hemothorax arising from a subpleural AVM of the upper lobe. There were multiple telangiectases in the tongue and the tonsils, as typically associated with Osler-Weber-Rendu disease (hereditary hemorrhagic telangiectasia, HHT). The post-mortem molecular genetic analysis proved the presence of a disease-causing mutation in the endoglin gene constituting a predisposition for pulmonary AVMs. According to the literature, almost half of the AVMs in the lung are seen in HHT patients. Based on the presented case and the relevant literature, the article addresses the forensic aspects of fatal hemothorax and the importance of detecting the source of bleeding.