A 32-year-old green-winged macaw (Ara chloroptera) was diagnosed with chronic lymphocytic leukemia based on progressive lymphocytosis and the presence of a monomorphic population of well-differentiated lymphocytes in the bone marrow of a clinically normal bird. Chemotherapy was initiated because of rapidly increasing peripheral lymphocyte counts. In addition to oral prednisone (1 mg/kg once daily), oral chlorambucil (1 mg/kg twice weekly) was initiated but was discontinued after 6 weeks because of thrombocytopenia. The leukocyte count was stabilized for 29 weeks with the concurrent use of oral cyclophosphamide (5 mg/kg 4 d/wk) and daily prednisone, and the bird exhibited a good quality of life. The bird died shortly after the chemotherapy was inadvertently discontinued. The neoplastic cells from this macaw stained positive for CD-3 antibody and negative for Bla.36, suggesting the leukemia was of T-cell origin. This is the first report of long-term treatment of a macaw with cyclophosphamide and documents thrombocytopenia in a macaw secondary to chlorambucil treatment.