This is a theoretical study of the inherent spatial resolution of the latent image on the surface of an amorphous selenium (a‐Se) plate used for diagnostic x‐ray imaging. The following effects are considered: (A) ranges of primary photoelectrons; (B) reabsorption of K fluorescence; (C) reabsorption of Compton scatteredphotons; (D) diffusion; (E) the geometric effect due to oblique incidence of x rays; (F) electrostaticeffect; and (G) the space charge effect. The modulation transfer function of a‐Se in the diagnostic x‐ray energy range has been estimated. In conclusion, (A) and (E) are the main factors limiting the resolution, and for diagnostic x rays, the inherent spatial resolution of a‐Se plates is much better than that of CsI layers used in x‐ray image intensifiers.