GROUND-BASED measurements of volcano deformation can be used to assess eruptive hazard, but require the costly (and often hazardous) installation and maintenance of an instrument network, Here we show that spaceborne radar interferometry, which has already shown its utility in mapping earthquake-related deformation(1), can be used to monitor long-term volcano deformation. Two families of synthetic aperture radar images, acquired from ascending and descending orbits by the satellite ERS-1, and looking at Mount Etna from opposite sides, cover the time period from 17 May 1992 to 24 October 1993, and include the second half of Etna’s most recent eruption, Despite artefacts of the interferometric technique, we can observe a volcano-wide deflation, which is an expected consequence of the eruption, but which had not previously been appreciated, We quantify it using a simple model based on the change of pressure in a sphere located in an elastic half-space; the modelled deformation increases linearly with time until the end of the eruption. Our results show that it will be possible to use this technique to detect the inflation of volcanic edifices that usually precedes eruptions.