This paper uses a mixed, quantitative and qualitative approach to analyze interaction between tourism development and conservation regulations on two World Heritage islands: Fraser Island (Australia) and the Curonian Spit (Lithuania). Both destinations are iconic areas attracting 300,000–400,000 visitors annually, which is 300–1500 times more than the number in the local population. Therefore tourism poses serious stresses on both conservation of heritage values and subjective wellbeing of local people. Complicating these pressures is the fact that at the same time, tourism provides a critical local driver of economic sustainability. Even though strict nature conservation and site management regulations are in place because both territories are protected as national parks and world heritage sites, a survey reveals that there is continuous pressure from local communities and from the tourism sector to renegotiate and alter the boundaries of the currently prescribed management framework. ‘Bending the rules’ is a widespread practice of actors at both sites. The focus is on understanding the pressures affecting sustainability in this broadest sense, with the goal of finding some balance between prescription and negotiation in management.