Primates are often considered problematic to house in mixed-species exhibits. Here, a successful exhibit for Goeldi's monkeys Callimico goeldii and Pygmy marmosets Callithrix (Cebuella) pygmaea is described. These species are sympatric in nature, although there has been no evidence of interspecific association between wild groups. Both species are arboreal but they diverge in significant ways in their ecological niches. Data were collected to determine the compatibility of these species and to examine how the enclosure space was utilized. Interactions mainly comprised C. goeldii approaching C. pygmaea and the latter reacting submissively. Callimico goeldii and C. pygmaea utilized the enclosure space (height and furnishings) differently from each other but in a similar way to that described for each species in the wild. This factor may contribute to the peaceful co-existence of C. goeldii and C. pygmaea in a mixed-species exhibit at Edinburgh Zoo.