Having grown faster than world GDP since the 1950s, international tourism is today one of the most important tradable sectors, with expenditure on tourist goods and services representing some 8% of total world export receipts and 5% of world GDP. Starting from a broad perspective, two main facts could be pointed out: a) countries specialised in the tourism sector have experienced in the recent past a good economic performance and b) they have a (relatively) small dimension. This paper examines these facts considering with particular attention the dimension point of view. We use a two-sector endogenous growth model to define the conditions required for small countries with a relative large endowment of natural resource to specialise in tourism and to enter the faster growth path. A model based on the size of the natural resource suitable for tourism development is presented and discussed.