Ground penetrating radar (GPR) was used to investigate the internal structure and development of an active parabolic sand dune in the Bigstick Sand Hills of southwestern Saskatchewan, Canada. The radar survey was conducted in a grid configuration using 250 MHz antennas. The radar frequency and the properties of the aeolian sands limited the penetration of the radar signal to the uppermost 4 m. Radar profiles parallel to the prevailing westerly wind reveal three zones with differing structural arrangements that are interpreted to represent three phases in the development of the dune: (1) underlying low-angle reflections representing preexisting aeolian strata associated with sand sheet or dune marginal deposition; (2) high-angle reflections representing downwind migration by grainflow; and (3) a variety of high- and moderate-to-low-angle reflections representing a more complex pattern of migration involving grainflow, grainfall, and ripple deposition. Radar profiles perpendicular to the prevailing wind are characterized by convex-up and concaveup reflections along the dune head and are interpreted as spur and trough structures, respectively. Radar profiles over the wings reveal an arrangement of high-angle reflections radiating away from the center of the dune. The main structural features from the radar profiles are summarized into two radar surfaces; three radar packages; and three radar facies, one of which has two subfacies. Observations of exposed surface stratigraphy following extensive wind erosion lend support to the interpretations made from the GPR data.