A seventeen-year-old girl was referred to the emergency department with dysphagia and dyspnea due to large swelling in the floor of the mouth after 20 days of evaluation. Magnetic resonance imaging shows a well-defined sublingual mass measuring 70 mm × 74 mm × 46 mm, causing severe oral and oropharyngeal space narrowing. The surgical excision of the lesion was performed through an intraoral approach under general anesthesia. Moreover, the pathologist reported a dermoid cyst. A dermoid cyst rapidly enlarging can lead to a life-threatening condition, particularly if they grow near main upper airway structures, so their resection in golden time has an especially clinical importance.