A coprological study to determine the helminth infections of horses in Istanbul was carried out. Individual fecal samples were taken from 204 horses (111 males and 93 females) of varying ages and breeds. The samples were examined for eggs by Fulleborn's flotation, Benedect's sedimentation methods and for the larvae of lungworm by the Baermann's method. Further individual larval cultures were performed from fecal samples for the identification of 3rd stage larvae (L3) of strongyle nematodes. It was found that 33(16.2%) of 204 horses were infected with any nematode species, 23(11.3%) with Cyathostomin nematodes, 17(8.3%) with cyathostomins except Gyalocephalus and Posteriostomum, 13 (6.4%) with Poteriostomum spp., 11(5.4%) with Strongylus edentatus, 7 (3.4%) with Trichostrongylus axei, 4 (2.0%) with Triodontophorus spp., 3 (1.5%) with Strongyloides westeri, 1 (0.5%) with Gyalocephalus capitatus, 1 (0.5%) with Oxyuris equi, 1 (0.5%) with Parascaris equorum, and 1 (0.5%) with Oesophagodontus robustus. Out of 204 horses, 15 (7.4%) were infected with only one species, 12 (5.9 %) with two species, 4 (1.9%) with three species, and 2 (0.9%) with four species. No trematode or cestode eggs could be detected.