PurposeThis paper aims to analyse the Portuguese companies’ determinants of capital structure. To reach this objective, the authors used data from 37 non-financial Portuguese large enterprises and from 4,233 non-financial small and medium enterprises for the period 2010-2016. Additionally, the authors selected a sub-period from 2010 to 2014 for a deeper understanding of the impact of the sovereign debt crisis and the Economic Adjustment Programme of Troika on the capital structure of those companies.Design/methodology/approachThree dependent variables were tested according to debt maturity, and a dynamic panel data model, namely, the generalised method of moments system estimator, was used to test the formulated research hypotheses following Arellano and Bover (1995) and Blundell and Bond (1998) to capture the dynamic nature of the firm’s capital structure decisions.FindingsIn general, the results point out that the capital structure decisions depend on a set of firm-specific factors, and that the effects of the determinants of the debt maturity ratios differ according to the type of firm, i.e. large/small firms, and the economic cycle.Originality/valueTo the best of the authors’ knowledge, this is the first study that has been carried out in Portugal by using two samples of large and small companies for analysing the effects of the Economic Adjustment Programme of Troika on the capital structure of companies. The authors seek to understand which type of companies suffered more because of the effects of the Economic Adjustment Programme of Troika during this period, and which are the capital structure determinants that present greater change. Contrary to what might be expected, large companies are the firms that suffer most from the Economic Adjustment Programme. Probably, because these companies are the most immediate, most scrutinised and those that must show abroad that the bank did not fund them in the long term, because of the imposition and limits to grant credit faced by the banks themselves.