Arctic sea ice is rapidly declining. The trend in sea-ice extent between 1979 and 2006, derived from satellite observations, was –9.1 ± 1.5% per decade. The recent record minimum in September 2007 increased this downward trend to –11.2% per decade. However, measurements of ice extent only tell one part of the story and to fully understand changes in the Arctic ice cover we must also understand how the ice thickness is changing. Radar and laser altimetry have shown a decline in sea-ice thickness following the 2007 ice extent minimum. We present satellite altimetry estimates of Arctic sea-ice thickness, updating the time series to include the winters up to 2009/2010, and separate thickness changes in the multi-year and first-year ice cover.