Amazona diadema is a parrot of the Brazilian Amazon basin between the Rio Negro and the Rio Solimões.
Adults are green, with black edging on feathers from the crown to the breast. The forehead and cere are red, the cheeks yellow-green, the tail green, and some secondary feathers red at the base. Juveniles have paler red on the forehead and lores and dark-brown irises.
In the wild it feeds mainly on fruit pulp, as well as nuts, seeds, flowers, buds, and leaf shoots. The World Parrot Trust says its flocking and roosting behaviour is assumed from the related Red-lored Amazon, so those behaviours are not included here.
An extinction-risk assessment has not been added yet.