This is the first documented case report of dermatitis associated with the poultry mite (Dermanyssus gallinae) in a horse. It occurred in a 16-year-old horse that was in contact with domestic hens. Clinical signs consisted of severe pruritus, with self-induced hair loss mainly on the head. Despite the multiple skin scrapings performed during both day- and nighttime, mites were only isolated from the in-contact poultry and from the horse's environment, and not the horse. The animal was treated using a 2% permethrin solution, sprayed on the entire body once a week for 4 weeks, and by decontamination of the horse's immediate environment. Although eradication of the mites and elimination of further contact between the horse and the poultry were not achievable, recurrence of dermatitis was prevented by regular applications of permethrin on the horse and biannual decontamination of the horse's stable.