The three‐dimensional boundary‐element method (3D BEM) has been discussed in some aspects involving the subdivision of boundary elements, the quadrature of surface charge density integrals, and their singularities. The 3D BEM has been applied to the analysis of nonrotationally symmetric perturbations in electrostatic lenses. The perturbations due to machining defects (including elliptical distortions, inclined end faces, misalignments, and their combinations) have been calculated and also the asymmetric aberrations have been computed. A set of computer programs has been developed. The computed perturbation potential distributions have been compared with the theoretical ones.