Large-flank instability has been proposed by most recent authors as a major process in the dynamics of Mount Etna. However, several aspects of the models are still disputed, such as the boundaries of the moving area and the driving force for the instability. In this paper we present synthetic aperture radar interferometric data which allow us to identify two main sectors of active instability where the deformational process differs. An eastern sector is bounded to the north by the Pernicana–Provenzana fault, to the west by the North Rift Zone and the South Rift Zone and to the south by the Mascalucia–Tremestieri–Trecastagni fault system. Interferograms provide new data on the activity and extent of the southern boundary, which was previously underestimated. In this sector the structural features indicate an eastward sliding, driven by E–W regional extension, which can be interpreted as a result of the retreating slab of the Ionian subduction. A second collapsing sector exists along the southern flank of Mount Etna, where the interferograms show the presence of an active anticlinal ridge. This ridge is interpreted as the result of southward gravity spreading over a basal decollement between Etna and its Plio–Quaternary basement and the Hyblean platform. The two sectors first became active in summer 1996, after the beginning of a new cycle of eruptive activity at the summit. The activity was ongoing until January 1998, with the deformation rate ranging from 4–6 mm/yr for the Mascalucia–Tremestieri–Trecastagni faults to 12 mm/yr for the anticlinal ridge.