The aim of this paper is to point out the other, less positive side of tourism, mass or overcrouded tourism. It is a topic that has become very popular over the past few years and has been talked about more and more, but not enough is being done at both local and national levels. Mass tourism is not only a challenge to poor countries or developing countries for which tourism is the main driver of the economy and income, but it is also a global challenge. In addition to general information on the characteristics of mass tourism, this paper analyzes the development of mass tourism in several tourist destinations around the world, which were selected as glaring examples of vulnerability due to excessive, uncontrolled tourism development, which is also the subject of this paper. The selected case analyzes will explain the impact and consequences of the mass development of tourism on tourist destinations, but also on the tourists who visit them. This topic is extremely important for the Republic of Croatia because Croatia is also in some destinations faced with the problem of mass tourist visits, especially at the peak of the tourist season. There is a conflict between the expected growth of tourism, which generates positive economic effects and the threat to tourist destinations due to such increased tourist traffic (which is mostly manifested in the threat to the environment and quality of life of the local population). For such destinations, it is extremely difficult to ensure long-term sustainable tourism development. The question that will be answered in this work is how it is possible to predict, prevent or mitigate the consequences of excessive tourism growth, what measures are recommended in such situations and what is necessary to take to mitigate the negative effects of mass uncontrolled tourism development.