The Pd-B system in the composition range of the solid solution PdB y has been the subject of a number of investigations as it provides an attractive model system for interstitial compounds. No consensus about the crystal structures and phase boundaries, particularly in the low-temperature regime, has been reached in the earlier works. In the light of very recent results on the crystal structure and composition ranges of the low-temperature phases, on the basis of X-ray, electron, and neutron diffraction analyses, a tentative phase diagram is presented which is compatible with practically all previous results. © Carl Hanser Verlag.