Simple SummaryCanine and human co-evolution have disclosed remarkable morphological plasticity in dogs. Brachycephalic dog breeds are increasing in popularity, despite them suffering from well-documented conformation-related health problems. This has implications for the veterinary caseloads of the future. Whether the recent selection of dogs with progressively shorter and wider skulls has reached physiological limits is controversial. The health problems and short life expectancies of dogs with extremely short skulls suggests that we may have even exceeded these limits. Veterinarians have a professional and moral obligation to prevent and minimise the negative health and welfare impacts of extreme morphology and inherited disorders, and they must address brachycephalic obstructive airway syndrome (BOAS) not only at the level of the patient, but also as a systemic welfare problem.AbstractThis article, written by veterinarians whose caseloads include brachycephalic dogs, argues that there is now widespread evidence documenting a link between extreme brachycephalic phenotypes and chronic disease, which compromises canine welfare. This paper is divided into nine sections exploring the breadth of the impact of brachycephaly on the incidence of disease, as indicated by pet insurance claims data from an Australian pet insurance provider, the stabilization of respiratory distress associated with brachycephalic obstructive airway syndrome (BOAS), challenges associated with sedation and the anaesthesia of patients with BOAS; effects of brachycephaly on the brain and associated neurological conditions, dermatological conditions associated with brachycephalic breeds, and other conditions, including ophthalmic and orthopedic conditions, and behavioural consequences of brachycephaly. In the light of this information, we discuss the ethical challenges that are associated with brachycephalic breeds, and the role of the veterinarian. In summary, dogs with BOAS do not enjoy freedom from discomfort, nor freedom from pain, injury, and disease, and they do not enjoy the freedom to express normal behaviour. According to both deontological and utilitarian ethical frameworks, the breeding of dogs with BOAS cannot be justified, and further, cannot be recommended, and indeed, should be discouraged by veterinarians.