Sustainable tourism is a dominant theoretical paradigm and the most acceptable solution to the challenges of modern tourism development. The main goal of the paper is to examine the achieved level of development of sustainable tourism in the Republic of Serbia on the example of spa destinations. Spa destinations are one of the three most developed forms of tourism in the Republic of Serbia with a long tradition of development. The paper analysed the most developed and recognizable destinations: Vrnjačka Banja, Sokobanja, Vrdnik Banja, Palić Banja, Bukovička Banja and Koviljača Banja. To assess the achieved level of sustainability, indicators developed by the European Union were used: economic, ecological, social, cultural and indicators of tourist satisfaction with the destination. The research results show that the achieved level of development is not aligned with sustainable development. The paper provides recommendations on how to improve the development of tourism and harmonize it with the principles of sustainable tourism.