The West Antarctic Ice Sheet flows seaward around and through the Ellsworth Mountains to feed the Ronne-Filchner Ice Shelf. A high ice-sheet surface, featuring a major inland divide, abuts the western mountain flank. The present-day grounding line of the Ronne-Filchner Ice Shelf is near the eastern mountain flank. Two major erosion glacial features characterize the Ellsworth Mountains. First, the exposed mountains show classic features of alpine glacier erosion. These are best developed in the Sentinel Range of the northern Ellsworth Mountains where cirque erosion has left horns, arêtes, and sharp spurs. Only the summit plateau of Vinson Massif (4,897 m) remains as undulating, pre-alpine topography. Well-developed alpine landforms also mark the Heritage Range of the southern Ellsworth Mountains. The West Antarctic Ice Sheet today engulfs many of the lower ridges of the Ellsworth Mountains. Second, a glacial trimline is etched into alpine ridges and spurs throughout the Ellsworth Mountains. Elevations of this trimline show a remarkably consistent pattern. In the Sentinel Range, trimline elevations generally diminish along the range north and south of where the high inland ice divide today abuts the mountains; they also decline from west to east across the range. Trimline elevations in the Heritage Range likewise show a consistent pattern, with higher values near the central, inland flank of the range and lower values to the east and south. Bedrock ridges above the trimline are serrated, whereas those below the trimline lack serrations, and some show glacial polish and striations. Drift patches and erratics occur below the trimline. We infer that extensive alpine glacial erosion of the Ellsworth Mountains antedated etching of the trimline. The trimline and striations together show major thickening of the West Antarctic Ice Sheet subsequent to this alpine erosion. Thicker West Antarctic ice flowed seaward around and through the Ellsworth Mountains. The major divide on the inland ice sheet maintained its present position and was 400 to 650 m higher than at present (ignoring isostatic compensation). Ice-surface elevations increased 1,300 to 1,900 m along the eastern mountain flank near the ice shelf (ignoring isostatic compensation). We infer that substantial grounding of West Antarctic ice occurred in the Weddell Sea embayment when the West Antarctic Ice Sheet stood at the trimline. We propose two widely opposing age models for ice-sheet expansion to the trimline. In one model the expansion is late Wisconsin/Holocene in age. In the other model the expansion is pre-late Quaternary, and perhaps Tertiary, in age.