ATmatrix is formulated to characterize scattering by a traction‐free periodic rough surface and numerical results for several surface profiles are presented. The normalized reflected intensities are computed, for the cases of longitudinal (P) as well as shear (SV) wave incidence, as functions of the angle of incidence and frequency of the incident wave. The anomalous behavior of the reflected waves are explained in terms of their conversion from evanescent to propagating waves, as well as in terms of Rayleigh surface waves. Hybridization of theT‐matrix scheme with a point‐matching procedure is also discussed.