A 2-yr-old female Brahma chicken was presented to the Poultry Mobile Clinic of the College of Veterinary Medicine at North Carolina State University with a 3-wk onset of a wet sneeze that progressed to wheezing with a whistle-type sound. Upon observation, a cyst was found above the left clavicle in the area around the crop. The bird was euthanatized due to the progressive and chronic nature of the symptoms. Postmortem examination revealed an ovoid, soft to fluctuant, smooth, pale brown mass (2 × 0.9 × 0.8 cm), encased within the cranial membrane of the left cervical air sac. Histologically, focally expanding the left cervical air sac was a pedunculated, nonencapsulated, well-demarcated, moderately cellular neoplasm that consisted of cuboidal cells predominantly arranged in variably sized cystic structures lined by a single layer of cells. Neoplastic cells have strong cytoplasmic immunolabeling against cytokeratin AE1/AE3. Gross and histologic findings were consistent with an air sac cystadenoma. Primary respiratory neoplasia in birds is infrequent. Air sac carcinomas, adenocarcinomas, and cystadenocarcinomas have been described in Psittaciformes, Columbiformes, Falconiformes, and Cuculiformes. Benign air sac tumors are poorly documented, and detailed descriptions of this neoplasm in poultry literature are lacking.