The potential of spatial planning to achieve sustainable development can be improved with expert input in the planning process. Vulnerability study provides knowledge about vulnerability of natural resources to development. Intense economic pressures in transition countries make sustainable spatial development especially challenging. Bosnia and Herzegovina is an example of transition country, which recognized the importance of knowledge support for planning and explicitly requires vulnerability studies as an input in the planning process. The environmental vulnerability study presented in this contribution was prepared for spatial plan for the Canton Sarajevo and will serve as a model case for other plans. Differently from prevailing ex ante use of vulnerability studies it was applied ex post, whereby the environmental compliance of the plan was assessed by overlaying it with vulnerability maps. The results have shown that although the objectives of the plan follow sustainability principles, its land use designation is much less environmentally oriented. An average of 25% of planned development involves areas, which are very vulnerable from one or more aspects. We propose to find alternative sites for these areas or to provide very strict regulations and conditions for building in detailed plans.