Avian gastric yeast (Macrorhabdus ornithogaster), formerly known as Megabacteria, is becoming increasingly prevalent in pet and breeding birds in the United States. This report describes a chronic M. ornithogaster infection in a cockatiel. The case history, clinical presentation, diagnostic procedures, and treatments are described. The M. ornithogaster infection resolved; however, the cockatiel continued to have chronic crop statis. Chronic infection with M. ornithogaster resulted in sclerosing ingluvitis in this case. A discussion of the morphology, clinical forms, antemortem and postmortem diagnoses, and treatments for Macrorhabdus ornithogaster follow.