The fatigue of copper single crystals, oriented for single slip, was studied using electron channelling contrast imaging (ECCI) in a scanning electron microscope. This technique allows the detection and characterization of dislocation structures in bulk specimens. This paper presents ECCI images showing dislocation arrangements associated with intrusions, extrusions and stage I and stage II cracks in single-crystal copper samples fatigued by tension-compression along [541]. The presence of intrusions or stage I cracks on the persistent slip band (PSB) planes caused no noticeable change in the local dislocation structures in the matrix vein and PSB ladder structures. Stage II cracks deviate from the PSB planes and were associated with elongated dislocation cells inclined in the direction of the loading axis. These elongated dislocation cells are confined to within 10 μm of the crack tip.