Investment in agricultural land in the developing world has rapidly increased in the past two decades. In Cambodia, there has been a surge in economic land concessions, in which long-term leases are provided to foreign and domestic investors for economic development. More than two million hectares have been leased so far, sparking debate over the consequences for local communities and the environment. Here we combined official records of concession locations with a high-resolution data set of changes in forest cover to quantify the contribution of land concessions to deforestation between 2000 and 2012. We used covariate matching to control for variables other than classification as a concession that may influence forest loss. Nearly half of the area where concessions were granted between 2000 and 2012 was forested in 2000; this area then represented 12.4% of forest land cover in Cambodia. Within concessions, the annual rate of forest loss was between 29% and 105% higher than in comparable land areas outside concessions. Most of the deforestation within concessions occurred after the contract date, and whether an investor was domestic or foreign had no effect on deforestation rates. We conclude that land acquisitions can act as powerful drivers of deforestation.