A 2-mo-old, female blue-and-yellow macaw (Ara ararauna) presented with severe abdominal distension, pain, and respiratory distress. Ultrasonographic examination detected a heterogeneous mass with multiple anechoic areas, compatible with a multilocular cyst, occupying most of the coelomic cavity. Postmortem examination revealed a mass of 12.0 × 8.5 × 5.0 cm, which had an irregular surface and was connected by a pedicle to the ileum. This mass compressed and displaced the liver, proventriculus, gizzard, and intestines cranially to the left. The cut surface was lobulated, gray-white, mildly firm or soft, and was interspersed with multiple cysts filled with viscous and opaque liquid. Microscopically, it was composed of well- differentiated embryonic tissues from the endoderm, mesoderm, and ectoderm; therefore, it was diagnosed as a mature teratoma, which was theorized to have originated from Meckel's diverticulum. This study is the first, to the authors' knowledge to report a case of a teratoma in a blue-and-yellow macaw.