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Reliability is one of the important factors in distribution planning and expansion. Due to high availability of components, input data in reliability assessment are fuzzy. In this paper an algorithm for reliability assessment in distribution systems is proposed with uncertainties in input data such as failure rates, repair times and operation of protective devices. By use of this procedure, reliability indices, membership functions of outage cost for load points, feeders and systems can be calculated. The proposed approach has been applied to electric network of north east of Tehran with satisfactory results.