Indonesia, like many other developing countries, is turning to ecotourism in an attempt to integrate the goals of development and nature conservation. Although ecotourism may be a valuable tool for preservation of biodiversity, it can have long-term negative effects on reserves, wildlife and local communities if improperly managed. In this study the authors evaluated ecotourism in the Tangkoko DuaSudara Nature Reserve, North Sulawesi, by examining trends in visitor numbers, the tourist experience, the distribution of tourist revenues, and tourist impact on the Sulawesi black macaque Macaca nigra and spectral tarsier Tarsier spectrum. The data collected showed that, although tourism is expanding rapidly, local benefits are not being fully realized, the reserve does not generate enough money to implement management, and primate behaviour is being affected. There is urgent need for a change in legal status of the reserve if ecotourism is to be managed. National park status would accommodate ecotourism planning and development, provide for greater participation by the local community, and allow for increased revenues for management.