A case of proventricular dilatation disease is described in a scarlet macaw (Ara macao) from clinical presentation to diagnosis with molecular methods. The initial clinical signs were depression progressing to head pressing over several days. A leukocytosis with toxic heterophil changes, hypoalbuminemia, and increased serum activity of aspartate aminotransferase and creatine kinase were present. Lead and zinc assays were within reference ranges, and results from Chlamydophila and polyomavirus testing were negative. Contrast-enhanced fluoroscopy revealed normal gastrointestinal transit times and motility as well as the presence of 2 small metallic foreign bodies in the ventriculus. The macaw was treated with antimicrobials, analgesics, vitamins E and B complex, force-feeding, and fluid administration with little improvement. Euthanasia was elected, and histologic examination of brain tissue revealed a perivascular lymphoplasmacytic infiltration, while the lungs had evidence of a fungal pneumonia. Tissue samples from the brain and proventriculus tested positive for the presence of Avian bornavirus genotype 2, while serology confirmed Avian bornavirus infection.