Dermoid cysts (DC) of the head and neck are relatively rare, presenting as a slow-growing and painless mass, usually located in the floor of the mouth at the midline. However, when they reach large proportions, they can cause dysphagia, dysphonia, and dyspnea. Herein, we report a case of a 23-year-old male presenting with a painless swelling in the floor of the mouth. Magnetic resonance imaging revealed the location of the lesion above the mylohyoid muscle, between the geniohyoid muscles. The patient was submitted to an excisional biopsy under general anesthesia, and histopathology revealed a cyst lined by a keratinizing squamous epithelium, containing adnexal structures in the wall, confirming the diagnosis of DC. There were no signs of local recurrence on the follow-up. DC should be considered in the differential diagnosis of the floor of the mouth swellings.