The structure and strength of fiber/matrix interfaces in fiber-reinforced composites are crucial in determining the overall mechanical behavior of these materials. To investigate the integrity and structure of such an interface on the microstructure scale, a model composite consisting of a single crystal Al(2)O(3) fiber in an Al matrix was investigated with X-ray microdiffraction. The intensity of the (30.0) and (22.0) reflections of Al(2)O(3) was monitored in topography mode using an X-ray beam focused by a tapered capillary to spot sizes ranging from 5 to 25 mum. Significant changes in this intensity revealed buried voids along a nominally intact interface. These changes also provided information about the distribution of residual stresses along the interface. The discussion includes advantages and some complications with this technique for measuring residual stresses in composites.