A 2-month-old, full-term female presented with a left upper neck mass that was first noted at birth. Her parents reported no fevers, constitutional symptoms, or enlargement of the mass. On physical examination, there was a nontender 4-cm mass in the left submandibular region with no overlying skin changes. Ultrasonography results showed an avascular cystic structure with internal debris and a single thin septation. Contrast-enhanced computed tomography (CT) of the neck soft tissue revealed a 3-cm low attenuation, nonenhancing, cystic-appearing mass that elevated the submandibular gland to the level of the parapharyngeal fat space with medial extension of the lesion into the tongue musculature. The walls were thin except for mildly thickened capsule along the posterior aspect of the lesion (Figure, A and B). Fluid that aspirated from the cyst was serous, and cytology showed mature and anucleate squamous cells with acute inflammation. The mass returned after 3 weeks. Further analysis 8 months after the initial CT via contrast-enhanced magnetic resonance imaging (MRI) showed a large, multiseptated cystic structure (Figure, C); the capsule of the wall was mildly thickened and was contrast enhancing. At age 12 months, the mass was excised via neck dissection. A lateral component at the level of the sternocleidomastoid muscle was completely excised. An intraoperative rupture of the thin capsule caused some spillage of cystic contents that were milky white in some areas and mucinous in others.