This paper presents the development of models and the analytical study of the structural response of deteriorating unbonded posttensioned beams, with the aim of providing suitable tools for the evaluation of existing deteriorated structures. The corrosion phenomena of the tendons are reviewed in the introduction. Two modeling approaches are proposed: (1) beam macro finite-elements (MFE) using cross-section analysis and (2) two-dimensional (2D) nonlinear finite-element (FE) analysis. The corrosion attack modeling considers tendon-breaking and ductility-reduction of the prestressing and mild steel. Bond deterioration is also considered for the ordinary reinforcement. The models are validated by simulating three tests on corroded beams with unbonded prestressing wires, part of the Rance benchmark exposed to 40 years of attack in a natural marine environment, and then tested for imposed loading in the laboratory. The results obtained for the global response show a good agreement with the tests at all stages of loading. The model’s predictions regarding the strain in the ordinary bars and unbonded wires are discussed in relation to the ductility reduction of the reinforcement caused by pitting corrosion and the risk of stress-corrosion cracking. Both modeling approaches are adequate, with different levels of discretization and size of the output. The MFE modeling is appealing for use in practice because of its computational simplicity.