Although congenital thumb absence has been reported frequently in humans,their occurrence in macaques is rare. We observed three cases of spontaneousthumb defects in captive female rhesus monkeys. One animal exhibited bilat-eral absence and two other presented unilateral thumb absence, all withmetacarpal integrity. This report presents the clinical, radiological, and gene-alogical details as well as possible etiologies in an attempt to draw a parallelwith humans and other primate species.