A certain class of structural problems at surfaces is readily accessible to investigation by x-ray photoelectron diffraction (XPD). This is usually the case for surface and interface geometries where core levels of specific atoms can be singled out from the XPD spectrum that are located below the topmost atomic layer. Other atoms are thus placed in a forward scattering geometry, and their relative positions are exposed by the associated forward focussing peaks. Prominent examples for such geometries are multilayer epitaxial film growth or intermixing phenomena at interfaces. Yet, there are important structural problems where such forward scattering geometries are often absent, like the internal structure of a single monolayer film, the registry of the film with respect to the substrate, or the adsorption geometries of atomic adsorbates. Over the last several years, various tricks have been devised that expand the scope of XPD to this kind of problems: -(i) For O/Rh(111) it has been demonstrated that the weak backscattering off the substrate atoms can reveal the exact bonding site of the atomic adsorbate. Prerequisites are a high atomic number of the substrate material and low temperature. -(ii) For well ordered monolayer films, the internal film structure can be determined by measuring first and higher order diffraction fringes. This is exemplified by the system of hexagonal boron nitride (h-BN) on Ni(111) as well as several alkali monolayer systems on Al surfaces. -(iii) When a monolayer film is strictly commensurate with the substrate and well ordered, the film structure and registry can be extracted from XPD data of a substrate signal, measured with and without the monolayer present on the surface. The resulting difference data sets need to be compared to simulated data resulting from multiple scattering model calculations. Again, the case in point is h-BN on Ni(111).