Transgranular slit-like voiding has been observed to cause fatal defects in electromigration- or stress migration-damaged Al submicron interconnects. To study the morphology and crystallographic characteristics of transgranular voids, we have tested single crystalline Al lines with various textures and in-plane orientations. Lines with (100), (110), and (111) textures were found to have triangular erosion voids along their edges. These voids were generally bound by {111} facets. While triangular erosion voids are frequently found in the lines, not all lead to failure of the lines. Some lines fail due to narrow, slit-like voids which are bound by {111} planes and lie along either <110> or <112> in-plane directions, depending on the orientations of the crystals relative to the orientations of the lines. Some of the slit-like voids are initiated along the erosion void facets. Similar void morphologies are observed in both unpassivated and passivated lines. Some of the lines have very large voids at the negative pad implying that voids are mobile. Through continued studies of the failure rates and failure morphologies of single crystalline lines, the mechanisms of transgranular failure of polycrystalline lines should be clarified.