A 37-year-old female yellow-headed Amazon parrot (Amazona ochrocephala oratrix) was presented after a 4-month-period behavior change and intermittent episodes of obtunded mentation. Clinical findings on physical examination included ataxia, a weak grasp, and reluctance to move. Results of magnetic resonance imaging were consistent with severe hydrocephalus without evidence of cerebrospinal fluid obstruction. The bird was treated with tapering dosages of prednisolone over a 4-month period, during which time the episodes did not occur. Discontinuation of treatment was attempted several times but resulted in relapse. After 3.5 years of maintenance treatment with prednisolone, the bird was presented subsequent to a 5-hour episode of obtunded mentation and worsening neurologic signs. Despite increasing the dose of prednisolone and providing additional supportive care, the bird's condition worsened, and euthanasia was elected. Necropsy findings included severe hydrocephalus with significant loss of right cerebral parenchyma and no evidence of cerebrospinal fluid obstruction. Histologic examination of the remaining cerebral parenchyma revealed a moderate, multifocal, cellular infiltrate; encephalomalacia; fibrosis; and hemosiderosis in tissue adjacent to the distended ventricles. Other findings included hepatic vacuolar degeneration. Diagnostic imaging and postmortem findings were consistent with a diagnosis of hydrocephalus ex vacuo. To our knowledge, this is the first report of hydrocephalus in an Amazon parrot as well as the first report of hydrocephalus in any avian species associated with long-term follow-up and prolonged corticosteroid treatment.