While traditionally people relinquish their pets to an animal shelter or pound, the internet provides a newer method to re-home. We analysed advertisements (ads) on the largest website in Australia for trading dogs and cats, gumtree.com.au. Data was collected in 2016. Dogs were sampled on February 7, 16 and 24, 2016 and cats on February 9, 19 and 26, 2016 with 2640 ads for relinquished dogs, and 2093 ads for relinquished cats. It was estimated >31,000 puppies/dogs and >24,000 kittens/cats are relinquished on gumtree.com.au per year. The median age of dogs was 1.42 and cats 0.9 years of age. There were 23% of dog ads and 62% of cat ads for free animals. Compared to the human population there were proportionately more ads in Queensland and fewer ads in Victoria. A total of 15 people were surveyed who had relinquished a dog or cat using gumtree.com.au. The dog owners used gumtree.com.au because they believed the shelters were full (n = 4), and; they wanted to see/interview the new owner (n = 2). For cat owners it was because they had originally got the cat on gumtree.com.au (n = 2); they use gumtree.com.au for other things, and it works (n = 2), and; they wanted to see/interview the new owner (n = 2). The data collected will be valuable for implementation of policy and interventions to protect the welfare of un-wanted dogs and cats.