Hemolymphangioma is a benign malformation of the lymphatic vessels. Cervical localisation is the most frequent. Mediastinal localisation is rare, but may be life-threatening because of airway compression. We report on a four-month-old boy who presented, in a context of epidemics, with clinical signs of acute bronchiolitis requiring mechanical ventilation for several days. Chest X-rays showed an important mediastinal mass with airways compression. Diagnosis was evoked on CT-scan aspects and confirmed by histology. Surgery allowed complete resolution, but dysphonia and oropharyngeal disorders persisted for several months. This rare congenital malformation is reviewed.