A 15-year-old female blue and gold macaw (Ara ararauna) was presented for evaluation after being found laterally recumbent, reluctant to move, and lethargic. Results of a complete blood count showed an increased number of immature heterophils with increased cytoplasmic basophilia and degranulation and the presence of a left shift. Radiographs and a computed tomography scan were performed and revealed a markedly enlarged spleen. An ultrasound-guided fine-needle aspirate of the spleen was submitted for cytologic examination and aerobic bacterial culture. While the culture revealed no growth, cytologic examination identified mononuclear phagocytes with cytoplasmic vacuoles containing structures consistent with bacteria. Pan-bacterial 16S rRNA polymerase chain reaction of the splenic sample followed by direct sequencing identified a Coxiella-like agent identical to one previously isolated in the liver of a golden-mantled rosella (Platycercus eximius). Phylogenetic analysis shows that avian coxiellosis agents and Coxiella burnetii, the agent of Q fever, represent 2 independent events of development of vertebrate pathogenicity in this group of tick endosymbionts. This report suggests diagnostic and treatment directions for coxiellosis in avian patients and indicates where further study is needed.