Interactions of indigenous peoples with the surrounding non-indigenous society are often the main sources of social and environmental changes in indigenous lands. In the case of the Suruí in Brazilian Amazonia’s “arc of deforestation,” these influences are leading to deforestation and logging that threaten both the forest and the sustainability of the group’s productive systems. The Suruí tribal leadership has initiated a proposal for an economic alternative based on Reducing Emissions from Deforestation and Degradation (REDD). This has become a key case in global discussions on indigenous participation in REDD. The realism of the baseline scenario that serves as a reference for determining the amount of deforestation and emissions avoided by the proposed project is critical to assuring the reality of the carbon benefits claimed. Here we examine the SIMSURUI model, its input parameters and the implications of the Suruí Forest Carbon Project for indigenous participation in climate mitigation efforts.