In this paper, the fatigue behavior of concrete subjected to combined stresses in the compression-tension region of the biaxial stress space is studied. Hollow cylindrical concrete specimens are subjected to combined stresses through torsional loading. The load-deflection responses of specimens subjected to cyclic and constant amplitude fatigue loading are presented. Damage imparted to the specimens during cyclic and fatigue loading processes was monitored using mechanical measurements and a nondestructive evaluation technique based on the measurement of structural resonance frequencies of vibration. The complete load response of the specimen subjected to cyclic loading was obtained by unloading the specimen at different points in the postpeak part (descending branch) of the quasistatic response. Changes in the resonant frequencies during the loading procedure were monitored. Fatigue tests were performed to failure with three different torsional load ranges. The decrease in rotational stiffness duringfatigue tests was obtained from mechanical measurements, and the resonance frequencies are presented. It was observed that the decrease in rotational stiffness at failure for the constant amplitude fatigue loading was comparable to the corresponding load in the postpeak part of the quasistatic response. The number of cycles to failure is closely related to the rate of the reduction of stiffness of the specimen as well as the resonant frequencies in linear portion of the fatigue response. This relationship is independent of the applied load range. The fatigue failure of concrete subjected to torsional loading is a local phenomenon similar to failure for quasistatic loading; the damage is seen to localize to a crack in the first few cycles, and the subsequent fatigue behavior is governed by the propagation of that crack. An approach for predicting the fatigue life and the stiffness of a pavement structure is finally presented using the results of this paper.