This paper reports prevalence of coccidial oocysts in fecal samples from 6 endemic and 2 introduced lizard species on Mauritius, an island nation in the Indian Ocean. Total coccidian prevalence was 54% (n = 341) for the endemic 'ornate day gecko,' Phelsuma ornata; 48% (n = 159) for the endemic 'Durrell's night gecko,' Nactus durrelli; 53% (n = 15) for the endemic 'Serpent Island night gecko,' N. serpensinsula; and 78% (n = 248) for the introduced gecko, Hemidactylus frenatus. These high prevalences may reflect lack of long-lasting immune response to coccidial infection. There were few significant differences in prevalence among age, island, sex, or body condition within species, suggesting that these coccidia are relatively nonpathogenic and have little effect on host fitness. Prevalence was higher in the dry season than the wet season. These data suggest other factors, such as low host immune response to reinfection, affect overall prevalence more significantly than the effect of humidity on oocyst survival on Mauritius. No coccidia were found in samples from the endemic 'Gunner's Quoin night gecko,' N. coindemirensis (n = 155), probably reflecting parasite extinction due to a host population bottleneck following historical introduction of rats. There was no evidence of competitive or facilitative interactions between Eimeria sp. and Isospora sp., but evidence of competition between 2 Eimeria species in the 'ornate day gecko,' Phelsuma ornata. No evidence was found of cross-species infection, suggesting that reptile coccidia have high host specificity and are, therefore, poor subjects for studies of parasite-mediated competition and the evolution of sex.