Birnesite-type MnO2 nanowires were prepared by direct reaction of NaMnO4 with ethanol under hydrothermal conditions. Changing the pressure vessel load allowed a layered oxide in the form of nanoflakes to be obtained. The resulting nanowires were 10–20nm wide and several micrometers long. Interestingly, the nanowires were poorly crystalline as revealed by their XRD patterns; also, they exhibited especially strong (100) reflections that were assigned to 1D growth of the particles. By contrast, the XRD pattern for the nanoflakes was consistent with an increased crystallinity as a result of 2D particle growth. The electrochemical properties of the nanowires and nanoflakes in 0.5M Na2SO4 were evaluated by cyclic voltammetry and galvanostatic charge/discharge testing in two- and three-electrode cells. The nanowires exhibited an ideal capacitive behavior and a higher specific capacitance than the nanoflakes (191 vs. 157Fg−1). In our opinion, the improved performance of the nanowires is a result of their high structural disorder and lattice strain rather than their higher specific surface area.