Establishing protected areas (national parks together with wildlife sanctuaries) in North Thailand did not reduce the likelihood of forest clearing, but wildlife sanctuaries may have reduced the probability of deforestation. Where new roads are located affects how much of a threat they are to protected areas.Using plot-level data, Cropper, Puri, and Griffiths estimate a bivariate probit model to explain land clearing and the siting of protected areas in North Thailand in 1986.Their model suggests that protected areas (national parks together with wildlife sanctuaries) did not reduce the likelihood of forest clearing, but wildlife sanctuaries may have reduced the probability of deforestation.Road building, by reducing the impedance-weighted distance to market, has promoted clearing, especially near the forest fringe.The authors simulate the impact of further road building to show where road building is likely to have the greatest impact on forest clearing and where it is likely to threaten protected areas.This paper - a product of Infrastructure and Environment, Development Research Group - is part of a larger effort in the group to examine factors affecting deforestation in developing countries. The study was funded by the Bank's Research Support Budget under the research project quot;Spatial Models of Environmental Processes: A Study of Deforestation in Thailandquot; (RPO 683-17). The authors may be contacted at [email protected], [email protected], or [email protected].