GROUND-based radar observations of Mercury have revealed unusually strong, highly depolarized echoes from the north1,2 and south2 poles. These anomalous echoes have been cited as evidence of polar ice deposits1-5. Thermal studies3-5 suggest that the permanently shaded floors of large polar craters are cold enough to preserve water ice in a stable state over aeons, in spite of Mercury's proximity to the Sun. Here we present high-resolution radar maps of Mercury's polar regions, derived from delay-Doppler measurements. We have resolved the north and south polar anomalies into numerous crater-sized features, and we have been able to identify the source craters for many of these features after making small corrections to the pole positions on the Mariner-10 images. The coincidence with crater locations, together with other properties of the radar features, are consistent with the polar-ice hypothesis.