Strontium cerate (SrCeO3) is the parent phase of a family of prototype proton-conducting perovskites with important potential applications as electrolytes in protonic ceramic fuel cells, hydrogen-separation membranes, and sensors for hydrogen and humidity. Apparent nonstoichiometric behavior and the microstructure of SrCeO3 have been investigated. Phase analysis by X-ray diffraction indicates that single-phase material in the system Sr1+xCeO3+delta is obtained for compositions x = 0.02-0.03 and that nominally stoichiometric SrCeO3 (x = 0) synthesized by either solid-state reaction or the citrate method is Sr-rich. Selected area electron diffraction confirms that the system crystallizes with the GdFeO3-type orthorhombic perovskite structure (space group Pnma). Structural defects characterized by high-resolution transmission electron microscopy include twin domain boundaries and SrO-rich, Ruddlesden-Popper-type planar defects. Magnetic susceptibility measurements down to 2 K indicate that the Ce3+ content is minor (similar to 0.01 mol per formula unit for slow-cooled material) and does not influence the observed nonstoichiometry.