In 2015, the United Nations High Commission for Refugees accommodated over 15 million refugees, mostly in refugee camps in developing countries. The World Food Program provided these refugees with food aid, in cash or in kind. Refugees' impacts on host countries are controversial and little understood. This unique study analyzes the economic impacts of refugees on host-country economies within a 10-km radius of three Congolese refugee camps in Rwanda. Simulations using Monte Carlo methods reveal that cash aid to refugees creates significant positive income spillovers to host-country businesses and households. An additional adult refugee receiving cash aid increases annual real income in the local economy by $205 to $253, significantly more than the $120-$126 in aid each refugee receives. Trade between the local economy and the rest of Rwanda increases by $49 to $55. The impacts are lower for in-kind food aid, a finding relevant to development aid generally.