On average, Latin American firms are small with respect to world patterns, both in terms of the quantity of assets they control and the amount of employment they generate. We examine data on firm size from developed and developing countries around the world to assess the influence of demand, supply and institutional factors on the size of the largest firms in each country. We find that, besides the size of the economy and the level of income per capita, the key determinants of the size of firms are trade openness, stock market capitalisation and physical infrastructure. Our simulations suggest that if the gaps with respect to the best Latin American performer were closed in each of these three areas, firm size in the countries of the region would – on average – reach world patterns.