Introduction: We describe the clinical course and emphasize the difficulties in diagnosing T-cell lymphoblastic lymphoma. The differential diagnostic difficulties have previously been described in regard to pneumonia, but to the best of the authors' knowledge this is the first case report to describe lymphoma in relation to trauma. Case presentation: A previously healthy 16-year-old Danish boy presented to our hospital with chest pain and accentuated protruding thoracic veins. Ten days prior to hospitalization he had suffered a blunt thoracic trauma while playing soccer. After drainage of an excessive amount of pleural fluid, he developed severe respiratory distress. A chest tube was inserted and he was transferred to a level 1 trauma centre. Here, a computed tomography scan unexpectedly revealed significantly swollen mediastinal and retroperitoneal lymph nodes, and he was later diagnosed with T-cell lymphoblastic lymphoma. Conclusions: This case emphasizes the importance of reacting to an unexplained large amount of pleural fluid after a patient suffers thoracic trauma and to consider possible underlying causes. This report is mainly addressed to emergency personnel, but it is also relevant to pediatricians, surgeons, anesthesiologists, and general practitioners.