After a long preparatory phase on Etna a network of 4 borehole dilatometers has been installed. This activity took place in two successive phases (2010-2011 and 2013) supported by two research projects. The borehole dilatometers are installed in holes drilled at depths usually greater than 100 m, and they measure the volumetric strain of the surrounding rock potentially with nominal precision up to 10-12 in a wide frequency range (10-7 – 102 Hz). In this paper we describe the characteristics of the equipment used, the methods for the borehole installations, and the problematic related to the instrumental working. We describe the results of the instrumental calibrations obtained by different methods after the installations. We illustrate the results obtained by the changes of strain...