Fatigue life and deformation are intimately related phenomena and a model involving a relationship between them can best be derived by methods that explicitly take vagueness into account. In this paper, the theory of fuzzy sets, especially fuzzy modeling, is employed to represent fatigue life and deformation relations as a set of fuzzy rules. A fuzzy logic algorithm has been devised for estimating the fatigue life from deformation measurements. The main advantage of fuzzy models is their ability to describe the knowledge in a descriptive human-like manner in the form of simple rules using linguistic variables only. In this manner the classical power relationship between the fatigue life and deformation variable can be replaced by a set of fuzzy rule bases. The fuzzy approach is applied for test data obtained in Isparta city, Turkey. © 2002 Elsevier Science Ltd. All rights reserved.