The contest is held in Petaluma, California, each year as part of the Sonoma-Marin Fair and has attracted a huge amount of media attention.
First established in the 1970s, organisers say it is held to “celebrate the imperfections that make all dogs special and unique”.
It now attracts audiences of up to 30,000 people, with the winner receiving $1,600, a trophy and a free trip to New York City.
In the 2022 edition Mr Happy, a 17-year-old Chinese Crested-Chihuahua mix from Arizona, took home the prize.
And there have been plenty so-ugly-they-are-adorable entries over the years.
Here are 19 of the dogs with faces only a mother could love.
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9. Princess Chelsea
Robert Rond holds his Chinese Crested dog named Princess Chelsea before the start of the 20th Annual Ugliest Dog Competition at the Sonoma-Marin Fair. Photo: Justin Sullivan
10. Monkey
Monkey, a Brussels Griffon owned by Scotch Hayley, walks along the red carpet during the World's Ugliest Dog Competition in 2016. Photo: JOSH EDELSON
11. Miss Ellie
Dawn Goehring, of Tennessee, holds her dog Miss Ellie, a Chinese Crested Hairless dog, during the 21st Annual World's Ugliest Dog Contest in 2009. Miss Ellie had previously won Animal Planet's World's Ugliest Dog contest. Photo: Justin Sullivan
12. Sweepie Rambo
Sweepie Rambo, a Chinese Crested, is held up by owner Jason Wurtz on his way to winning the 2016 World's Ugliest Dog Competition. Photo: JOSH EDELSON