Numerical studies of second-harmonic generation of beams with aberrations based on the solution of three-dimensional propagation equations including diffraction and walk-off effects are reported. Because of aberrations of the fundamental wave, the refractive index of an extraordinary wave, the phase-mismatch angle, etc. will vary across the aperture, and results of these studies show that these variations can lead to changes in conversion efficiency, transverse intensity distribution, and phase distortion of the second-harmonic beam. The second-moment radius and the divergent angle of a second-harmonic beam are presented. It has been found that second-harmonic beams are less divergent than fundamental waves, but the M-2 factor can be either worse or better. The calculated results of different orders of Zernike aberrations are given. (C) 2002 Optical Society of America.