The authors acknowledge the support of the Office of Basic Energy Sciences of the United States Department of Energy. Determination of an interface damage function (IDF) from a stereological procedure similar to that presented by Hilliard is described. The mathematical and experimental simplicity of the method is utilized in measuring an IDF for polycrystalline copper crept at 0.6T sub m under uniaxial tension. Whereas previous work focused on a five parameter description of the local state of a grain boundary, the domain of the IDF is increased to eight degrees of freedom in the present study to include the complete geometrical description of grain boundary structure. The resulting functions identify certain types of grain boundaries which were preferentially damaged. Most of the damage occurred on interfaces oriented nearly normal to the principal stress axis. Some relatively small angle boundaries demonstrated a surprising propensity to cavitate as did certain special boundaries distinguished by a group multiplicity in misorientation space greater than one. A sequence of two dimensional projections through the eight-dimensional domain of the IDF is shown to identify a number of interface structures which are readily damaged.