Is tectonic uplift or climate change the primary driving force behind continent-scale erosion? Here we examine these two hypotheses for tropical South America by comparing a high-resolution record of terrigenous sediment accumulation rates from the western tropical Atlantic Ocean with continental tectonic reconstructions and both low-latitude and high-latitude climate indices that span the past 13 m.y. Over the full record, terrigenous sedimentation rates most closely follow lowland aridity (as recorded by abundance ratios of terrigenous oxide minerals), an indication that basin-integrated climate is an important control of erosion. Step-like transitions in the flux and composition of terrigenous material near 8 and 4.5 Ma, however, follow dated tectonic events, which suggests progressive expansion of the drainage basin into less humid or less vegetated regions that were more prone to erosion. On long time scales, high-latitude climate variability and sea level (as recorded by δ18O) do not closely track terrigenous sedimentation. We conclude that regional climate change provides a mechanism for long-term erosion of tropical South America; tectonics plays a significant, but secondary, role in this area, perhaps by shaping the drainage basin to include regions in which the climate is more favorable to erosion.