To evaluate the gastro-intestinal parasite fauna of the wild Polish primitive horses (Equus caballus gmelini Ant., forma silvatica Vet.), 11 yearlings captured in the Reserve according to the control rules of population dynamics were diagnostically dewormed with abamectin+praziquantel. Expelled parasites were collected from the faeces 24, 36 and 48 hours after treatment. Among a total of 4456 specimens (a mean 405.1 per horse) 27 nematode species, one cestode and one species of botfly larvae were recovered. Strongylids were 100 % prevalent and represented by 24 species (2 large strongylid and 22 cyathostome species). Five cyathostome species (Cylicodontophorus bicoronatus, C. insigne, Poteriostomum imparidentatum, Parapoteriostomum mettami and Gyalocephalus capitatus) were recorded for the first time in Polish primitive horses, whereas two species (Cyathostomum montgomeryi and Cylicostephanus bidentatus) were found for the first time in the horse in Poland. Oxyuris equi was found in 100 % and Parascaris equorum in 63.6 % of yearlings surveyed. Tapeworms (Anoplocephala perfoliata) were revealed in 72.7 %, while Gasterophilus intestinalis instars in 90.9 % of horses. At least three parasite species were highly prevalent (i.e. S. vulgaris, A. perfoliata and G. intestinalis), which might be a reason of serious abdominal disorders in Polish horses living freely in the reserve.