Transmission electron microscopy observations of as-cast samples of an Al-Li-Cu icosahedral quasicrystal allowed us to demonstrate planar and line defects. By means of dark-field and weak-beam imaging techniques, planar defects were tentatively identified as π-type boundaries and low-angle subgrain boundaries, while line defects were found to be isolated dislocations. All the characteristics of the defects were determined by conducting extensive tilting experiments and performing conventional extinction contrast analyses. In particular, the isolated dislocations were found to have a Burgers vector aligned along a fivefold symmetry axis in physical space and to be screw in character.