An electron paramagnetic resonance (EPR) study of synthetic diamond crystals grown at HTHP conditions in the carbonate medium Na2CO3CO2H2OC has revealed a hydrogen-containing center (VOH) along with centers OX1, OX2, and OX3 tentatively associated with oxygen. In the X-band EPR spectra, the forbidden transitions of the center are superimposed on the allowed HFS lines of one hydrogen atom. We have succeeded in analysis of the allowed transitions in Q-band experiments. On the basis of the obtained experimental data a hypothetical model of the center has been proposed as a vacancy–oxygen complex with incorporated hydrogen atom. The occurrence of hydrogen in the studied diamond crystals is supported by the presence of CH vibrations in the IR spectra in the range of 3000 cm−1.