Background <p>Mediastinal masses are relatively common in pediatric populations, but their coexistence with bronchogenic cysts is extremely rare. Such cases present diagnostic and therapeutic challenges owing to overlapping features and the need for precise identification to guide appropriate management. Reporting this unusual combination enhances awareness and contributes to the understanding of their clinical presentation and treatment.</p> Case presentation <p>A 15-year-old female of Iranian ethnicity presented with a 3-month history of persistent, nonproductive cough unresponsive to standard medical treatments. The patient had no significant past medical history. Diagnostic imaging, including chest X-ray and computed tomography scans, revealed two separate thoracic lesions suggestive of mediastinal and pulmonary masses. The patient also underwent surgical resection via left posterolateral thoracotomy. Histopathological examination confirmed a mature cystic teratoma in the mediastinum, containing various tissue types, and an infected bronchogenic cyst within the lung, characterized by alveolar hemorrhage and abscess formation. Postoperative recovery was uneventful, and follow-up imaging demonstrated no residual abnormalities.</p> Conclusion <p>This case revealed the importance of comprehensive diagnostic evaluation in pediatric patients with persistent respiratory symptoms. Although rare, the simultaneous occurrence of mediastinal mature teratomas and bronchogenic cysts should be considered in differential diagnoses to enable timely surgical intervention. Recognizing this coexistence can lead to favorable outcomes and informs clinicians about the potential complexity of thoracic masses in adolescents.</p>