This paper presents an expert system-based methodology to evaluate impacts of voltage sags on industrial power systems from the end user point of view, in order to make decisions based on financial assessment. Causes and effects of the phenomena are analyzed and different mitigation solutions are taken into account. Three industries are studied and results show the best cost-effective solution for each case. In order to evaluate all information required for the methodology, a graphic software tool is designed as a platform to introduce new evidence to the Bayesian structure, to update costs involved and to present results in a simple way.