An umbrella cockatoo (Cacatua alba) and two cockatiels (Nymphicus hollandicus) were presented with rapidly enlarging masses of the head or wing joints. Historic trauma to these areas was confirmed in two cases. All birds were >2 yr of age, and two were female. Cytologic examination of fluid aspirated from masses in two cases was described as serosanguineous cytologically but failed to reveal inflammation, neoplasia, or microorganisms. Radiographic evaluation of these masses included proliferation and lysis of bone, suggestive of a neoplastic process. Histopathologic examination of surgically excised tissues revealed proliferative new bone and an absence of neoplastic tissue in all cases, consistent with aneurysmal bone cyst formation. Despite the guarded prognosis reported for other companion animals, these case results suggest a good prognosis for aneurysmal bone cyst in psittaciformes. Complete surgical excision and histopathologic examination is recommended for definitive diagnoses of aneurysmal bone cyst. Postoperative bandaging and rational antibiotic use are indicated to prevent excessive motion and secondary infection of affected sites, respectively.