Using a panel of 91 countries over 20 years, this study looks at possible overpopulation effects on the growth rate of per capita real Gross Domestic Product (GDP). Population variables are divided into two distinct concepts: density and growth. The primary goal is to measure a non-linear impact of population density on economic growth when density is defined as population per area of arable land. It is argued that, at the country level, there may be significant diseconomies of agglomeration coming from overcrowding effects. The secondary goal is to measure the impact of population growth on per capita real GDP growth. The current literature is conflicting about this effect and this analysis provides an empirical example for a fairly recent period. Empirical results do not support a significant impact of density on economic growth and an ambiguous impact for population growth is found.