Prothrombin 20210 G>A mutation is the second most frequent inherited factor increasing the risk for developing venous thromboembolism (VTE). The risk for VTE in homozygous carriers of this mutation is not well studied because of their rarity are rare. We report a case of a homozygous carrier of prothrombin mutation: a young man with massive pulmonary embolism, and his family - an asymptomatic homozygous sister, heterozygous parents with asymptomatic mother, and father with history of deep venous thrombosis (DVT). To our knowledge, this is the first reported case of homozygous prothrombin mutation carriers in Bulgaria and the other Balkan countries. We conclude that the homozygous prothrombin mutation creates predisposition for VTE that can manifest or not depending on additional factors, one of which could be male gender.