We use aerogravity data to estimate the water depth of subglacial Lake Vostok in East Antarctica. The inversion produces the first bathymetry map covering the entire lake. Lake Vostok consists of two sub-basins separated by a ridge with very shallow water depths. The deeper southern sub-basin is approximately double the spatial area of the smaller northern sub-basin. The close correlation between the pattern of basal melting and freezing and the bathymetric structure has important ramifications for the water circulation and the sediment deposition. We estimate the lake volume to be 5400 ¿ 1600 km3.