The blue-headed macaw is 41 cm (16 in) long. It has mainly green plumage (often tinged olive, esp. below) with the head, flight feathers and primary coverts blue. The uppertail has a maroon base, a narrow green center and a blue tip. The undertail and underwing are greenish-yellow similar to that of several other small macaws (e.g. red-bellied and golden-collared macaw). The medium-sized bill is pale greyish-horn with a black base (extent varies, but upper mandible in adults typically appears mainly pale). The iris is whitish with a narrow, often barely visible, maroon eye-ring. Unlike most other macaws, the facial skin and lores are dark greyish. The legs are dull pinkish. Juveniles resemble adults, but with the entire bill black, greyer legs, darker iris and the facial skin and lores white.