[en] The secondary extinction related to the neutron or x-ray diffraction in mosaic crystals is analysed in the framework of the transport theory. The initial transfer equations, valid for a general type of crystals, are first simplified on the assumption that all the diffracted radiation are registered. Then these equations are solved for a general anysotropic model of crystal microstructure. The final solution is simplified while choosing definite models of mosaic distribution. It permits to obtain practical correction formulas for secondary extinction