Discovery of several new specimens of the gigantic Eocene ground bird Diatryma gigantea from the Willwood Formation of northwestern Wyoming, has prompted an analysis of its feeding apparatus and an assessment of the mode of life of this unusual bird. Diatryma exhibits many of the features predicted by biomechanical models to occur in animals delivering large dorsoventral bite forces. Similarly, the mandible of Diatryma, which was modeled as a curved beam, appears well equipped to withstand such forces, especially if they were applied asymmetrically. Interpretation of these size-independent biomechanical properties in light of the large absolute skull size of Diatryma suggests a formidable feeding apparatus. The absence of modern analogues complicates the determination of just how this unique skull morphology correlates with diet. Suggestions that Diatryma was an herbivore seem improbable in that they require the postulation of excessively high safety factors in the construction of the skull. The traditional hypothesis of Diatryma as a carnivorous bird accords as well or better with the data at hand. Carnivory raises the probability of “accidental” encounter with bones, thus explaining the high safety factors. In fact, the skull and mandible of Diatryma are so massive that bone crushing may have been an important behavior. Diatryma could have been a scavenger. However, limb allometry and phylogenetic interpretation of limb proportions call into question the picture of Diatryma as a slow, plodding graviportal animal, suggesting that active prédation was within its behavioral repertoire.