Abstract Nine ponies (20 months of age) with naturally acquired cyathostome and pinworm infections were treated orally with ivermectin at a dosage of 400 μg /kg. Ivermectin was highly effective on the cyathostome infection. However, adult Oxyuris equi were present in six horses. In recent years, anthelmintic treatment with macrocyclic lactones have not appeared to deliver the expected efficacy against equine pinworms (Oxyuris equi) in the USA. This is the first European study to demonstrate anthelmintic resistance in Oxyuris equi to macrocyclic lactones in naturally infected ponies (Czech Republic).