Introduction: Venous thromboembolism is rare among children and has a multi-factorial aetiology. It’s important to establish the diagnosis and evaluate the functional prognosis. Case report: A previously healthy 11 year old adolescent was observed in the emergency room with clinical signs of superficial venous thrombosis of the upper limb. Laboratorial evaluation showed a sedimentation rate, coagulation study, autoimmune antibodies and homocysteine with normal values. Testing for heritable thrombophilia revealed prothrombin mutation (G20210A, heterozigosity) and mutation of PAI-1 (4G e -844A), both of which are associated with hypercoagulable state and indication to do prophylaxis with low molecular weight heparin in higher risk situations. Discussion/Conclusion: The rarity of thromboembolic events at this age and the atypical localization lead to an exhaustive laboratorial evaluation. Thrombophilia mutations may clinically become evident in adolescence, and its detection is important because of children’s lifestyle and the need of prophylactic treatment in some situations.