A 9-year-old male timneh African grey parrot (Psittacus erithacus timneh) was presented because of inability to fly and suspected trauma. The owner also had observed dyspnea, with tail bobbing and open-beak breathing. On clinical examination, a hard, painful mass was palpable in the left proximal humerus and axillary area. Radiographs revealed a radiodense soft tissue mass of the left humerus with no bony involvement, multifocal opacities in lung and air sacs, and an enlarged spleen. An asymmetric, vascularized cyst was detected in the mass by ultrasound examination. Results of biopsy of the mass revealed multifocal cysts composed of unilayer isoprismatic cells laying in vascularized connective tissue. Because of the severity of clinical signs and the poor clinical condition, the bird was euthanatized. On postmortem examination, the findings were air sac cystadenocarcinoma involving the humeral air sac with metastases in the spleen and kidneys, atherosclerosis, pneumoconiosis, and mycotic granulomatous pneumonia and airsacculitis with isolation of Aspergillus niger.