Average microstructural parameters and the extent of microstructural heterogeneity in nickel deformed at a high strain rate have been characterized quantitatively and compared to those after compression at a quasi-static strain rate. The microstructure in the high strain rate sample was found to be more refined and less heterogeneous than that in the sample compressed at a low strain rate. The greater refinement in the former sample was achieved due to subdivision by a high frequency of finely spaced low-angle boundaries.