Superior mediastinal syndrome is a life-threatening pediatric oncological emergency that requires high level of awareness and clinical suspicion to avoid misdiagnosis and devastating outcomes. Early diagnostic evaluation and management of underlying etiology are of utmost significance for optimal results. In children, it is most commonly caused by non-Hodgkin's lymphoma and T-cell lymphoblastic leukemia. We report a case of a six-year-old boy with superior mediastinal syndrome secondary to T-cell acute lymphoblastic leukemia, initially misdiagnosed as foreign body aspiration and underwent a procedure with a life-threatening outcome.