Yorkshire terriers are tiny dogs, belonging to the toy group of American Kennel Club classifications. Some very small Yorkshire terriers are being bred, but they aren't a special, recognized breed. The AKC doesn't recognize a breed standard for teacup Yorkshire terriers, or mini.
Smallest of the Small
According to the AKC's breed standard, a Yorkshire terrier for show isn't to exceed 7 pounds. Some Yorkies weigh more and some less, but most weigh 4 to 7 pounds. For some people, less is more, so breeders have responded by breeding smaller Yorkies. Because there's no breed standard for a "teacup" Yorkie, the definition is fluid. One breeder might consider a 4-pound dog a teacup, but others might strive to produce 2- or 3-pound dogs.
No matter how small Yorkies are, these guys possess large personalities and big voices. A Yorkie is a terrier, so he's smart, curious and trainable. His small size makes him ideal for apartment living, but he still needs a good daily walk to help burn off some of his high energy. The Yorkie is an affectionate, loyal dog who benefits from firm, gentle training. Lack of training and authority can result in a poorly socialized pup who takes over the house.
Though tiny, Yorkies can rack up some big vet bills. Most live healthy lives, but they are vulnerable to a few conditions. Bronchitis, eye infections, tooth decay and intolerance to anesthetic are common among Yorkshire terriers. They have a high incidence of a liver defect, portosystemic shunt, which often is surgically treated. Small Yorkies -- what you might think of as a "teacup" -- are especially prone to hypoglycemia, a swift drop in blood sugar. Bone structure is also a potential problem with super-small Yorkies; their bones are more fragile and their tiny ligaments and tendons are more prone to injury than those of larger Yorkies. This puts them at increased risk for hip dysplasia, slipped kneecaps, collapsed trachea and sprained or broken bones.
Small, medium or large, your Yorkshire terrier's long, flowing coat requires regular grooming. He'll need to be combed at least weekly, if not daily. An easier-to-maintain cut will require regular trips to the groomer. Yorkies are cold-natured, and if your dog is extra-small you need to take care to keep him warm. If the temperature drops below 68 degrees he'll appreciate a sweater, because tiny Yorkies are missing a healthy layer of protective fat. Regular vet visits are a must, and an understanding of the needs of a hypoglycemic pup is critical.