In this work, the concept of fuzzy fault currents (FFC) is introduced for modeling the uncertainties associated to conventional fault current analysis. In order to compute FFC, a general procedure for calculating functions of type-1 and type-2 fuzzy numbers is presented. This technique, which is based on extension principle and interval arithmetic, can be applied to several engineering problems where calculating functions of uncertain variables is required. The proposed methodology is used to compute FFC for a real distribution system. The results are shown and the advantages of the approach are discussed.