A quantitative post mortem study of 150 horses from Victoria was conducted to determine the prevalence and epidemiology of gastrointestinal parasites. A total of 42 species of metazoan parasite was found. The following species of non-cyathostome parasite were found (% prevalence): Trichostrongylus axei (51%); Habronema muscae (13%); H. majus (2%); Draschia megastoma (5%); Gastreophilus intestinalis (81%); G. nasalis (29%); Parascaris equorum (5%); Anoplocephala perfoliata (29%); Fasciola hepatica (0.7%); Oxyuris equi (7%); Strongylu vulgaris (23%); S. edentatus (23%); S. equinus (3%); Craterostomum acuticaudatum (7%); Triodontophorus serratus (8%); T. tenuicollis (8%); T. brevicauda (3%). Ninety-five per cent of horses were infected with gut-wall encysted stages of cythostomes with a mean intensity of 113,000 larvae per horse. Ninety-three per cent of all horses harboured adult cyathosome worms; 24 species representing 6 genera were found. The 3 most prevalent species were Cylicostephanus longiburstatus (76%); Cyathostomum catinatum (68%) and Cylicocyclus nassatus (54%). Seventeen species of strongyle were present in high abundance, which allowed their site distribution in the large intestine to be determined. Twelve species preferred the large colon to the small colon and caecum, and the remaining 5 species preferred the caecum. Statistical analysis of the parasitological data set allowed effects of sex, age, type, and physical condition of the horse as well as the season and environment on the prevalence and mean intensity of infection to be determined.