These are the extremes: the world's tallest dog Gibson (7 ft / 2.1 m tall when standing on his hind legs) has met Boo Boo (4 in / 10 cm high) the world's smallest dog in Sacramento, California for Guinness World Records Day 2007.

No doubt, the Chihuahua, a dog race that has its origins in northwestern Mexico, delivers the world's smallest pooches. The purpose of this event was to decide on which is the world's smallest Chihuahua/dog.

One and a half-year-old, Boo Boo, a long coated Chihuahua, of just 4 inches (10 cm) tall and weighing just 1.5 pounds (675 g) has been crowned in September as the new smallest living dog in the world by height by the Guinness Book of World Records.

Boo Boo outranked Ducky, a smooth coat Chihuahua, a "giant" 4.9 inches (12 cm) tall. Still, Ducky, weighing just 1.4 pounds (650 g), is the world's smallest dog by weight.

"Boo Boo was fed with an eye dropper every 2 hours, when she was born, and weighed just 1 ounce (28g)." said Boo Boo's owner Mrs. Lana Elswick of Raceland, KY. "I think that's one reason why people started raising such big Chihuahuas; it's very tedious to raise them small like Boo Boo, the way they are supposed to be", she said. "People say Chihuahuas are miserable and evil. I think they're really sweet, and if you want to go some place, you can just throw him in your pocketbook.", said Ducky's owner Lisa Messier.

Still, the world's smallest dog ever, as recorded by Guinness Book, was not a Chihuahua but a dwarf Yorkshire terrier, just 2.8 inches (7 cm) tall.

Instead, in the competition of the giant dogs, two breeds compete: the Great Dane, known for their gentle personality, and the Irish Wolfhound. By 2007, the Great Dane is ahead, with Gibson detaining the record since August 2004.

The 170-pound (77 kg) 5-year-old "Harlequin" Great Dane has a shoulder height of 42.6 in (107 cm) when on all four. Even if as tall as a lion or tiger, like all Great Danes, Gibson is very friendly.

Gibson is a real star that starred in various shows, from "Oprah Winfrey Show" to "Larry King Live". "He just puts a smile on people's faces. In one split second, people forget their cares and worries." said Gibson's owner, Sandy Hall of Grass Valley, California, USA, who characterizes the giant dog of being a "couch potato" and said her dog grew so big in a growth spurt between 4-12 months old.

Still, the heaviest dogs belong to the Swiss breed Saint Bernard. The largest individual was Duke, which belonged to Dr. A. M. Bruner from Oconomowuc (US) and had 135 kg (390 pounds) (as big as an average black bear) when he died in 1965.