International experience in environmental protection planning suggests that conservation projects can be successfully realized only if associated to socio-economic promotion, while taking account of possible distortions in the distribution of benefits. Furthermore, participation of local people both in management and in planning is often indicated as crucial. In this paper we consider an unsuccessful case, the Gennargentu National Park in Sardinia. We set up and test an econometric model to explain the decision of the local communities to accept or refuse their inclusion in the Park area. Results suggest that while different perceptions of new economic opportunities can possibly influence the decision, also political and cultural motivations are significant. A strong interaction between policy makers and local people is then recommended both at policy design and implementation stages.