Sustainable tourism is gaining importance in national agendas to encourage economic growth, social inclusion, and the protection of cultural and natural assets. More than 13 million tourists (10.6 mil. Romanians and 2.6 mil. foreigners) visited Romania in 2019, the fifth consecutive year of growth for the tourism sector. The authors have selected 10 statistical indicators to highlight the main components for tourism sustainability by using the principal component analysis (PCA). The current patterns of sustainable development of tourism and the territorial inequalities at a micro-scale were assessed based on a sustainable tourism index (STI). In addition, to observe the way indicators interact and determine each other and to analyze the territorial disparities, the hierarchical ascending classification was used. The study was performed using the statistical data available at NUTS5/LAU level provided by the National Institute of Statistics. In addition, various data and information extracted from documents published by the UNWTO, National Institute for Research and Development in Tourism, the World Bank, EUROSTAT, etc., were also used. By applying an STI, the authors were able to assess the tourism development level at a national scale in Romania, delineating the most advantaged/disadvantaged areas. The analysis of sustainable tourism in Romania shows that tourism performance is more consolidated in the big cities, the Black Sea coast, the Danube Delta and the Carpathian Mountains. Studies such as the present one are meant to provide a methodological framework that will be useful to perform a quantitative assessment of the sustainable level of tourism development in terms of economic, social and environmental performance.