A 16-year-old female umbrella cockatoo (Cacatua alba) was presented for a fluctuant, right-sided cervical mass that extended from the caudolateral edge of the right mandible to the coelomic inlet. Results of initial diagnostic tests were consistent with a cystic mass containing hemorrhage. Surgical exploration and removal of the mass was done, but because the hyoid apparatus was incorporated in the base of the cyst, complete surgical excision was not possible. Histopathologic results were consistent with a branchial cyst with carcinoma. Five months after surgery, the cockatoo exhibited intermittent periorbital swelling and epistaxis, and cytologic results of a fluid aspirate from the right infraorbital sinus were consistent with carcinoma. Results of magnetic resonance imaging revealed extensive abnormal T2 and short-tau inversion-recovery hyperintense tissue associated with the right side of the head and neck, infiltrating between muscle planes and extending into the right retro-orbital tissue and nasal cavity. At 7 months after surgery, the bird was severely dyspneic and was euthanatized. To our knowledge, this is the first report describing the diagnosis, management, and histologic characteristics associated with a branchial cyst with carcinoma in an animal.