A 19 years-old woman, on her 17th week of pregnancy presented to the emergency department with thoracic pain and vomiting. An empyema was diagnosed and she was transferred to a tertiary hospital for treatment. After drainage of the empyema a mediastinal mass was detected and a thoracic MRI revealed a multicystic lesion of the anterior mediastinum, causing cardiac and left lung compression, suggestive of a complicated teratoma. After a multidisciplinary discussion involving pulmonology, radiology, obstetrics and thoracic surgery, she was operated successfully by clamshell incision. A mature complicated teratoma was resected and a left pleurectomy/decortication performed. She was discharged on day 17 with no obstetrical or respiratory symptoms..