We examine the possibility to study hydrogen-bonded structures through core ionization energies. We use a recently derived self-interaction corrected density functional theory method where the core ionization energies for all chemically shifted elements are obtained by a single calculation of the ground state of the structures. A direct dependency between the hydrogen atom to acceptor atom bond length and the chemical shift of the core ionization energy of the acceptor atom is found, something that has rami. cations for the possibility of effective predictions of hydrogen bond lengths in hydrogen-bonded systems. This observation is verified by the conventional, much more time-consuming, self-consistent field calculations based on density functional theory. (C) 2008 Elsevier B.V. All rights reserved.