We report the case of a 13-year-old male presenting with recurrent symptoms of respiratory distress after a trauma of the lower limb. Pulmonary symptoms had been misinterpreted for several weeks and only marked symptoms of deep venous (DVT) and caval vein thrombosis later prompted the correct diagnosis of DVT and embolic events and subsequently a successful thrombolytic therapy. The case reported here shows a diagnostic pitfall of pulmonary embolism in an adolescent. It emphasizes the need to consider the possibility of thromboembolic events also in young children and adolescents presenting with atypical pulmonary symptoms and suffering from pulmonary diseases not responding to antibiotic therapy. In addition, although the homozygous PT A20210A gene mutation is a rare defect and its relevance as a risk factor on its own remains to be elucidated, this case suggests that a complete thrombophilia laboratory workup should be performed in young patients with a first symptomatic thromboembolic onset.