Sustainable tourism has been on the agenda since the publication of the Brundtland Commission Report in 1987. The concept of sustainable tourism focuses on tourism from economic, social and environmental aspects. The objective of this research paper is to examine the performance of two mass tourism destinations with regard to sustainability. It analyzes which sustainability factors that are considered most important to tourists visiting those mass tourism destinations. Moreover, a comparison between the opinions of the national tourists with the ones of the international tourists as well as the data collected from the two destinations. A quantitative questionnaire was handed out to tourists at a number of tourist offices in Rimini, Italy, and on the island of Rhodes, Greece. The questionnaire contained scales measuring the tourists’ satisfaction with the destination and their hotels from a sustainability point of view. The tourists also graded the level of importance to those factors. The main conclusion of the paper is that there is a difference between the tourists’ view on sustainability value at the two mass tourism destinations.