International trade flows are highly concentrated in the top units of analysis. In this paper, we study the firm-size distribution of Portuguese exports of goods over the period 1993-2017 and examine its impact on aggregate volatility. We fit power law relations using three different methods. The estimated Pareto exponents of Portuguese firm-level exports are very small, pointing to an extreme concentration of export values in the largest firms. Moreover, the Pareto estimates tend to decrease over time. We then investigate if the granular behaviour of aggregate outcomes of Gabaix (2011) is present in Portuguese firm-level exports. The results show that the idiosyncratic shocks to the largest firms may have significant effects on the dynamics of total exports.