A 25-year-old female macaroni penguin (Eudyptes chrysolophus) was diagnosed with exophthalmos secondary to retrobulbar neoplasia through use of computed tomography (CT). Histopathologic examination of the mass supported a diagnosis of malignant round cell neoplasia. Immunohistochemical (IHC) labeling was applied to determine cell origin; the neoplastic cells did not label with T-cell marker CD3 or B-cell marker BLA.36 and could not be further characterized. The scleral ossicles precluded evaluation of the retrobulbar space by ultrasonography; therefore, CT scanning is recommended for examination of intraorbital structures in penguin and other avian species.