Using plot level data, we estimate a bivariate probit model to explain land clearing and the siting of protected areas in North Thailand in 1986. The model suggests that protected areas (national parks and wildlife sanctuaries together) did not reduce the likelihood of forest clearing; however, wildlife sanctuaries may have reduced the probability of deforestation. Road building, by reducing impedance-weighted distance to market, has promoted clearing, especially near the forest fringe. We simulate the impact of further road building to show where road building is likely to have greatest impact and where it is likely to threaten protected areas. (JEL Q23, Q28, R40)