A 4-year-old girl presented with a floor-of-mouth mass. MRI showed a midline, T2 hyperintense, well-circumscribed mass superior to the mylohyoid muscle and splaying the geniohyoid muscles (Figs. 1 and 2). Several nonenhancing ovoid nodules with restricted diffusion were present in the anterior section of the lesion. Differential diagnoses included dermoid or epidermoid cyst, plunging ranula, and lymphatic malformation. Post-resection pathology demonstrated findings indicative of a dermoid.Dermoid cysts can contain fat, hair follicles, or other skin appendages and are lined by a keratinizing squamous epithelium. In contrast, epidermoid cysts are lined by a simple squamous epithelium and surrounding fibrous connective tissue. Dermoid and epidermoid cysts arise from the first and second branchial arches after sequestration of surface ectodermal tissue. The rare teratoid cyst contains elements of all three germ cell layers [1,2]. The location of these lesions with respect to the mylohyoid muscle is important for determining the most appropriate surgical approach. These benign lesions are equally common in boys and girls and typically present in infancy as painless masses. Surgical resection is curative.