The St. Bernard is a very large dog with a large head. A full-grown male can weigh between 160 and 260 lb (73–117 kg) or more and the approximate height at the withers is 27½ inches to 35½ inches (70 to 90 cm).
St. Bernards, like all very large dogs, must be well socialized with people and other dogs while young if they are to be safely kept as a pet. A St. Bernard not properly introduced to and socialized with children from a young age poses a threat, not having learned to distinguish between a child and other, smaller animals.
Extremely loyal, the St. Bernard is eager to please its owners. Due to its large adult size, it is essential that proper training and socialization begin while the St. Bernard is still a puppy, so as to avoid the difficulties that normally accompany training large animals. An unruly St. Bernard may present problems for even a strong adult, so control needs to be asserted from the beginning of the dog's training. While generally not as aggressive as dogs bred for protection, a St. Bernard will bark at strangers and their size makes them good deterrents against possible intruders.
The very fast growth rate and the weight of a St. Bernard can lead to very serious deterioration of the bones if the dog does not get proper food and exercise. Many dogs are affected by hip dysplasia or elbow dysplasia. Osteosarcoma (bone cancer) has been shown to be hereditary in the breed.
St. Bernards are susceptible to eye disorders called entropion and ectropion, in which the eyelid turns in or out. The breed standard indicates that this is a major fault.
The breed is also susceptible to epilepsy and seizures, a heart disease called dilated cardiomyopathy, and eczema.
Due to the likelihood of heath problems in later years, the average lifespan for a Saint Bernard is around 7–10 years.
