Hydrogen can be located in metal hydride structures by X-ray diffraction even in the presence of heavy elements, but the determination of accurate metal-hydrogen bond lenghts requires neutron diffraction on either hydride single crystals or deuteride powders. For ab-initio determinations of new metal hydride structures, a combination of high-resolution X-ray (synchrotron) and neutron powder diffraction is the method of choice. Studies are presented that illustrate the power and limitations of these methods.