In polycrystalline metals, plastic deformation is accompanied by lattice rotations resulting from dislocation glide. Following these rotations in three dimensions requires nondestructive methods that so far have been limited to grain sizes at the micrometer scale. We tracked the rotations of individual grains in nanograined nickel by using three-dimensional orientation mapping in a transmission electron microscope before and after in situ nanomechanical testing. Many of the larger-size grains underwent unexpected lattice rotations, which we attributed to a reversal of rotation during unloading. This inherent reversible rotation originated from a back stress-driven dislocation slip process that was more active for larger grains. These results provide insights into the fundamental deformation mechanisms of nanograined metals and will help to guide strategies for material design and engineering applications.