The development of indicators to measure sustainable tourism and to assist in the decision-making process of tourism destination managers has been a constant concern of some international organizations. However, at the European Union level, the tourism statistics system only states that Member States should collect and transmit harmonized statistics on tourism demand and supply, not referring specifically to sustainable tourism indicators. The main objective of this article is to analyse the tourism statistics system in Portugal, from 2001 to 2018, in order to understand how sustainable tourism has been viewed at this level and in a country which tourism activity has evolved significantly. The study, exploratory in nature, used a longitudinal quantitative approach, by performing a content analysis of the activity reports of the National Institute of Statistics, as well as methodological documents of the statistical operations of tourism. The results show that, in Portugal, the statistical system lacks indicators to measure and monitor the sustainable development of tourism in the country.