Animal hoarding is considered to be an under-reported problem, which affects the welfare of both people and animals. Few published studies on animal hoarding are available in the scientific literature, particularly outside North America. The present study was designed to obtain data on animal hoarding in Spain, with a particular focus on animal welfare issues. Data were obtained retrospectively from 24 case reports of animal hoarding involving a total of 1,218 dogs and cats and 27 hoarders. All cases were the result of legal intervention by a Spanish humane society during the period from 2002 to 2011. Hoarders could be characterised as elderly, socially isolated men and women who tended to hoard only one species (dog or cat). Most cases presented a chronic course of more than five years of animal hoarding. The average number of animals per case was 50, with most animals being dogs. In 75% of cases the animals showed indications of poor welfare, including poor body condition, and the presence of wounds, parasitic and infectious illnesses. Amongst the hoarded animals aggression and social fear were the most commonly reported behaviours. To the authors’ knowledge, this is the first report on animal hoarding in Spain and one of the first in Europe. Further studies are needed to fully elucidate the epidemiology, cross-cultural differences and aetiology of this under-recognised public health and welfare problem. More research might help to find efficient protocols to assist in the resolution and prevention of this kind of problem.