A finite element human thorax model was developed for predicting thoracic injury and studying the injury mechanisms under impact. Digital surface images of a human skeleton and internal organs were used to construct the three-dimensional finite element representation of the rib cage, the heart, the lungs, and the major blood vessels. The mechanical properties of the biological tissues in this model were based on test data found in the literature. The constitutive equations proposed in the literature for describing the mechanical behavior of the heart and the lungs were implemented in the code for modeling these organs. The model was validated against cadaver responses for both frontal and lateral impact. Good correlation between the model and the cadaver responses were achieved for the force and deflection time-histories.