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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1. Reggie
Reggie is presented before judges during the World's Ugliest Dog Competition in 2015. Photo: JOSH EDELSON
2. Pork
Pork, a 13-year-old male Chihuahua with blue painted nails, is presented to judges by owner Monica Huerta during the World's Ugliest Dog Competition in 2015. Photo: JOSH EDELSON
3. Yoda
Yoda was the winner of the 23rd Annual World's Ugliest Dog Contest in 2011, winning $1,000 in prize money. Photo: Justin Sullivan
4. Chu
Chu sticks his head between bars before competing in the World's Ugliest Dog Competition in 2015. Photo: JOSH EDELSON