Tourist seasonality is one of the main imbalances in the mass-destinations. This article seeks to provide more information on seasonality through an analysis of the situation in Catalonia, the most important Spanish region with respect to international tourism. This work focuses on a specific inspection of the main empirical factors. To achieve this, the traditional model of tourism demand has been used primarily as a reference, before an empirical application of a dynamic panel data model of markets for the 2000–2014 period (specifically using the GMM–DIFF model). Results reveal the significance of the inertial factor and the relevance of income and price factors, as well as observable behavioural differentials for some of the main source markets. We believe that the results obtained may be interesting with respect to tourism policies. Keywords: Tourist Seasonality; Dynamic Panel Data Models; Catalonia. JEL Classification: L83, C52.