A numerical analysis of free roll vibrations of a delta wing in an ideal incompressible flow (wing rock) is performed by solving the coupled dynamic and unsteady-aerodynamic equations. A computational algorithm is constructed on the basis of the vortex-lattice method. For regimes of self-induced vibrations, the calculation results agree well with experimental data. The nature of the damping function and specific features of its formation during the first vibration cycle are discussed. The excitation mechanism of self-induced vibrations is considered on the basis of wing vortex structure analysis. The effect of the nondimensional frequency and wing moment of inertia on the amplitude of self-induced vibrations is studied.