Thirlwall's Law is found to be the necessary but not sufficient condition for balanced long-run growth. A simple equation is considered whose empirical analysis could confirm – or reject – the validity of the Law. The analysis, conducted by means of econometric co-integration using the Dynamic Ordinary Least Squares method applied to data for 59 countries covering the years 1960-2012, suggests that Thirlwall's Law may not hold for the decisive majority of countries.