A primate community was studied in a fluvial tropical rain forest island, in the northernmost part of Brazilian Amazonia, in the State of Roraima. Density and biomass were determined, and the differences between the forest types were assessed. The line-transect method was used from the east towards the centre of the island. No previous studies had been carried out in this remote undisturbed area. Density and biomass varied between the forest types, as well as between frugivorous primates; the smaller-bodied species were more abundant in the forest that was richer in fruiting trees, while they were absent from a monodominant forest. The folivorous, or partly folivorous, primates were abundant in those forests with less fruiting trees. The abundance of the primates in the different forest types was shown to be a function of food availability.