The Beckmann-Kirchoff (B-K) classical scalar diffraction theory is commonly used in the scatter community to model and predict scattering behavior when surfaces are 'rough.' However, although the B-K theory can be used to model surfaces that are much rougher than other theories can handle, the B-K theory has a small-angle assumption inherent in its derivation. The paper illustrates a modified B-K theory that shows excellent agreement with experimental scattering data from rough surfaces for both large angles of incidence and scatter angles.