The structure and composition of the superconducting oxide YBa2Cu3O7−xhave been examined in atomic detail by field ion microscopy and imaging atom‐probe mass spectroscopy. The field ion samples were prepared from hot‐pressed disks of the oxide powders. Atomic resolution images were obtained with either argon or hydrogen as the imaging gas. Individual layers of atoms were observed which could be field evaporated in a uniform, layer‐by‐layer manner. Imaging atom‐probe analysis of the field ion tips indicated a metal composition which varied noticeably from sample to sample and an oxygen concentration which was consistently much too low.