The Bullmastiff is an English breed of dog of mastiff type and large size, with a solid build and a short muzzle.

Dogs had to have a minimum of four generations of descent from Bullmastiff stock without input from either Bulldog or Mastiff; cross-bred animals could not be registered.

[7][failed verification] A 2024 UK study found a life expectancy of 10.2 years for the breed compared to an average of 12.7 for purebreeds and 12 for crossbreeds.

[8] Health concerns within the breed include hip and elbow dysplasia, progressive retinal atrophy, bloat, and cancer, with a relatively high incidence of lymphoma and mast cell tumours.

[9][10][11] Bullmastiffs are prone to certain hereditary diseases, including: An autosomal dominant form of progressive retinal atrophy is common in the breed.