Megabacteriosis is a common cause of illness and death in exhibition budgerigars. The clinical signs are variable but include weight loss, difficulty in swallowing, vomiting, diarrhoea and sudden death due to haemorrhage. Significant lesions are confined to the proventriculus which becomes inflamed, dilated and ulcerated, and loses its normal architecture, and to the gizzard in which there are degenerative changes in the koilin layer.