A 19-yr-old intact female variable flying fox (Pteropus hypomelanus) presented with lethargy, behavior changes, and substantial weight loss. Initial clinical pathology revealed hypoglycemia and reduced ionized serum calcium, and imaging, including computed tomography, did not lead to a diagnosis. An adrenocorticotropic hormone (ACTH) stimulation test revealed baseline and post-ACTH cortisol concentrations that were lower than reported normal baseline cortisol concentrations in this species. Treatment with prednisolone resolved the clinical signs and laboratory abnormalities. Repeated attempts to decrease the prednisolone dose caused recurrence of clinical signs and weight loss. Based on diagnostic test results and response to therapy, a diagnosis of atypical hypoadrenocorticism was made.