The present study was undertaken to investigate the prevalence of Cryptosporidium infection in horses used for recreational riding as well as in humans. A total of 106 faecal specimens from horses raised in 4 localities of western Poland and 6 stool samples from 3 persons who had constant or sporadic contact with horses were screened microscopically for oocysts using modified Ziehl-Neelsen staining. Enzyme immunoassay (EIA) was additionally used for the detection of coproantigen in human stool samples as well as in 43 randomly selected horse faecal samples. The overall infection rate of horses determined by microscopic examination was 9.4%. To our knowledge, this is the first report of cryptosporidial infection in horses in Poland. The infection was identified only in adult horses raised on 2 of 4 examined farms. The intensity of equine cryptosporidial infection was light, as a rule. None of the infected horses appeared clinically ill. The real overall infection rate in horses could be higher. Among 43 faecal specimens additionally processed by EIA, 5 samples were positive both for oocysts and coproantigen, whereas in 7 faecal samples only the parasite coproantigen was detected. The morphometric analysis of oocysts indicated that the horses were most probably infected with C. parvum. Of 3 examined persons, cryptosporidial infection was identified in a rider who had sporadic contact with horses.