Abstract: A method based on wave optics for the determination of assembling tolerances of optical imaging systems, especially non rotationally symmetric systems, is given. The light emitted from an object point and its propagation in a system with assembling errors is described through wave fronts. Wave front changes due to free space propagation are calculated with Frenel's diffraction formula and those due to passing through a lens are calculated with equivalent amplitude transmittance function of the lens. A final imaging wavefront thus obtained is used to analyse the imaging performances, and the assembling tolerances can then be determined by making reference to some predetermined image quality requirements. An imaging system comprising two cylindrical lenses is taken as an example, and a formula for determining the tolerance of the non orthogonity between the generating lines of the two lenses is deduced. It can be seen that the present method is able to resolve problems that do not easily permit themselves to be analytically resolved with geometrical optics.