Trichomoniasis, a digestive tract disease of raptors caused by ingesting the protozoan Trichomonas gallinae of infected columbid prey, recently was reported to be common in and an important agent of mortality among urban nestling and fledgling Cooper's Hawks (Accipiter cooperii) in Arizona. However, the prevalence of T. gallinae in wild raptor populations is poorly documented. During 2000 we detected T. gallinae in only three (2.7%) among 110 nestling Cooper's Hawks at 48 nests in both urban and rural habitats in Wisconsin, North Dakota, and British Columbia. Mortality attributable to trichomoniasis among 5- to 22-month-old Cooper's Hawks was zero in the three combined study areas. Prevalence of infection by T. gallinae seems to vary greatly among nesting Cooper's Hawks across this raptor's continental breeding range.