Vulnerability to drought is the degree to which a system is susceptible to damage by drought and incapable of coping with its adverse effects. This article presents a method to calculate drought vulnerability indices in the Northwest River Basin System, Mexico. The method is based on the concept of vulnerability developed by the Intergovernmental Panel on Climate Change (IPCC, 2007), which differentiates three components of vulnerability: degree of exposure, sensitivity and adaptive capacity. Each of these components is represented by a set of relative indicators at the municipal level that allow for the determination of three basic types of vulnerability: economic, social and environmental, which converge in overall vulnerability. The successful use of the method in the Northwest River Basin System shows that it can be applied to the rest of river basin systems in Mexico, and it can also be adapted to be used at the state or national level. The strength of the method lies in its approach as an objective analytic procedure that makes it possible to identify the most vulnerable municipalities from economic, social and environmental perspectives, which is useful in managing resources and efforts to reduce vulnerability to drought in the different regions of the country.