Atoxoplasma spp. (extraintestinal Isospora spp.) are coccidian parasites that infect a variety of passerine species. Atoxoplasmosis has been difficult to diagnose using buffy coat and organ impression smear examinations or histopathologic examination of tissues at necropsy. The prevalence of this parasite was studied in the tanager collection of a zoological park after the death of several tanagers from confirmed and suspected infections. A polymerase chain reaction assay was used to test blood, feces, or tissue samples (or all) from 88 individuals representing 18 species. Twenty-three of 60 (38.3%) blood samples from clinically healthy birds tested positive for Atoxoplasma, and one of six fecal samples was positive. Nineteen of 32 (59.4%) tissue samples from deceased tanagers tested positive. A total of 57 other institutions were also queried regarding the presence of Atoxoplasma. The high number of Atoxoplasma-positive clinically healthy birds suggests that the parasite is prevalent subclinically within tanager collections, with young birds and stressed adults being the most likely to develop clinical disease. Thorough disinfection of enclosures, consideration of enclosure designs, and preventing fecal contamination of food and water are important methods of decreasing transmission. Selective breeding programs and regular screening of breeding pairs may be recommended to decrease transmission to susceptible offspring. Care should also be taken when housing tanagers in mixed species or in outdoor enclosures because the transmission risks between species have not been well established.