Ecotourism shows great potential for primate conservation, but further investigation through an ethnoprimatological lens is vital to understanding species-specific variation in human–nonhuman primate interactions at ecotourism sites. This study measured the rates and types of human–monkey interactions, the participants in these encounters, and the association between tourist numbers and interaction rates with white-faced capuchin monkeys (Cebus imitator) and mantled howlers (Alouatta palliata) at the Curú Wildlife Refuge in western Costa Rica. I collected data through 15-min all-occurrence samples for human–monkey interactions between January 2006 and December 2007. I recorded and analyzed a total of 1949 discrete interactions, representing one tourist group and one non-tourist group for each species. For both species, tourist groups showed more varied and more intense—but not more frequent—human–monkey interactions than the non-tourist groups. White-faced capuchins differed from mantled howlers in their greater frequency and more variable forms of human–monkey interactions. White-faced capuchins also showed a more gregarious pattern of interactions than mantled howlers, with most capuchin interactions being initiated by the monkeys and involving multiple actors. Although mantled howler human interaction rates correlated positively with levels of human traffic, white-faced capuchins did not show this relationship. These findings demonstrate that the differences in human–monkey interactions across species are an important consideration for the management of primate tourism sites. This study suggests that species-specific guidelines for ecotourism would reduce visitor impact on nonhuman primates.