An 18-year-old female Bali mynah (Leucopsar rothschildi) was presented for polyphagia, weight loss, and incoordination. Diabetes mellitus was diagnosed based on the history and clinical findings, including persistent hyperglycemia with concurrent hypoinsulinemia and glucosuria. A treatment protocol was developed that led to improvement of clinical signs and management of hyperglycemia over several months. Because of the advanced age of the animal, difficulty in maintaining euglycemia, and the stress of handling and treatment, euthanasia was elected 167 days after initial presentation. At postmortem examination, no pancreatic lesions were detected histologically that would account for the diabetes mellitus. To our knowledge this is the first reported case of diabetes mellitus and clinical management of this condition in a passerine species.