Sea-ice freeboard heights for all 18 ICESat campaign periods from March 2003 to October 2009 in the Weddell Sea are derived from ICESat laser altimeter measurements. Freeboard is combined with snow depth on the sea ice from AMSR-E passive microwave data and nominal densities of snow, water and sea ice to estimate sea-ice thickness. Sea-ice freeboard and thickness distributions show clear seasonal variations which reflect the yearly cycle of the growth and decay of the Weddell Sea pack ice. During the Antarctic winter (October–November), sea ice grows to its seasonal maximum both in area and thickness, filling in the Weddell Sea. For the winter periods, the mean freeboards are between 0.33 and 0.41 m and the mean thicknesses are between 2.1 and 2.2 m. During the Antarctic summer (February–March), thinner sea ice melts away; sea ice is mainly distributed in the west Weddell Sea near the Antarctic Peninsula. For the summer periods, the mean freeboards are 0.34–0.45 m and the mean thicknesses are 1.6–2.1 m. During the Antarctic fall (May–June), large areas of new thinner sea ice form over the Weddell Sea. For the fall periods, the mean freeboards and thicknesses vary from 0.26 to 0.28 and 1.3 to 1.5 m, respectively. The interannual differences in freeboard and thickness in three different seasons, the area and volume for each period are also described. Thickness results from the assumption that the ICESat freeboard equals to snow depth and the influence of ‘negative freeboard’ are also discussed. This study demonstrated the ability of satellite laser altimetry to monitor sea-ice mass balance, an important indicator of climate change.