Hydrocephalus is rarely diagnosed in pet birds, and when it occurs, a cause is rarely identified. Communicating hydrocephalus is described in an adult Goffin's cockatoo (Cacatua goffini). Marked cerebral atrophy without evidence of inflammation was observed grossly and histologically in the bird in this report. The segmentally hypertrophied arachnoid membrane provides a cause for the hydrocephalus and corresponding cerebral atrophy. Metaplastic change in the leptomeninges leading to communicating hydrocephalus is characteristic of vitamin A deficiency in other species. Such a deficiency was supported in this case by characteristic changes in the integument and a history of an all-seed diet. Improved recognition of hydrocephalus in pet birds combined with an accurate dietary history is essential to establishing the prevalence of such changes and to confirm our proposed mechanism of neurologic disease.