The objective of this research is to estimate the potential effects of migration on residential energy use and CO2 emissions in Hanoi, Vietnam, a location in which urbanization and migration are occurring simultaneously. This article estimates the effects of migration on residential energy use and CO2 emissions quantitatively, basing the probability of being a migrant on the economic, demographic and dwelling characteristics of households. The results of this study indicate that the effects of migration involve reductions in energy consumption and CO2 emissions. Urban-to-urban migration is shown to have no statistically significant impact on per capita energy consumption and CO2 emissions, which indicates that population increases through urban-to-urban population growth and natural population growth have no statistically significant differences in this regard. However, rural-to-urban migration is shown to have a significant and negative influence on residential energy consumption and CO2 emissions. Population growth led by rural-to-urban migration produces lower energy consumption estimates than natural population growth. Thus, energy consumption estimates are lower when a city's population increase is caused by rural-to-urban migration than when urban-to-urban migration and natural population growth are the main drivers of population increases. These results have important policy implications for developing urban cities regarding population growth and energy consumption.