Summary An epidemiologic study of shigellosis was the preliminary step in the formulation of a plan for the control of devastating infectious diseases in nonhuman primates at the National Zoological Park. Data were collected from primate groups with enzootic shigellosis and included the following species: white-cheeked and siamang gibbons (Hylobates concolor and H syndactylies); lion-tailed, celebes, and Barbary macaques (Macaca silenus, M nigera, and M sylvanus); black and white colobus monkeys (Colobus guerzea); grey-cheeked mangabeys (Cerecocebus albigena); spider monkeys (Ateles susciceps robusuts); ruffed lemurs (Lemur varrigatus); lowland gorillas (Gorilla gorilla); and orangutans (pongo pygmaeus). Data included results of physical examination, proctoscopy with biopsy, fecal parasitologic and cytologic examinations, and bacteriologic culturing of swabbed specimens of rectum and gingiva. Repetitive fecal examinations were subsequently performed and included bacteriologic culturing of fecal specimens for enteropathogenic bacteria and parasites and cytologic examination of feces. Data were collected for a 1-year period from 82 primates, and 14 gibbons were studied intensively. White-cheeked and siamang gibbons shed Shigella flexneri sporadically, but persistently. All gibbons were affected with a mean point prevalence of 30.7% (range 0 to 71%). Shigella flexneri also was isolated from feces of lion-tailed macaques. Shigella sonnei was isolated from feces of grey-cheeked mangabeys, celebes macaques, and spider monkeys. Of 180 colonic mucosal biopsy specimens from 60 primates, 3 contained Shigella spp. Most S flexneri isolates were serotype Y. Our findings substantiated that enzootic shigellosis was more widespread at the National Zoological Park than signs of disease and results of a few bacteriologic cultures suggested. Those primate species affected were pinpointed, and the heterogeneity of Shigella spp involved was elucidated. Supportive diagnostic techniques were investigated and an unconventional protocol for performing bacteriologic culturing of fecal specimens was found useful in decreasing false-negative results. Epidemiologic findings and shedding patterns defined appropriateness of clinical management options.