This article compares and analyzes land use and income diversification among two distinct groups of farmers in the Brazilian Amazon: recent colonists in Ouro Preto do Oeste, Rondônia, and traditional long-term residents along the Tapajós River, Pará. We investigate the hypothesis that farmers who diversify their cash income sources clear less forest on an annual basis, and we compare these livelihood choices across colonist and traditional populations. In particular, we develop a conceptual model based on the household production framework and use econometric models to identify determinants of diversification and forest clearing. We find that diversification of agricultural cash crops is negatively correlated with forest clearing by colonists, providing limited evidence for the hypothesis. Other significant covariates of diversification and forest clearing include cash income levels, stage in family life cycle, cattle ownership, and chemical inputs. Differences in these variables, and differences in household response to these variables, explain variation in diversification and forest clearing across the two populations.