The spatial distribution of soil gas radon activity was studied along the Pernicana Fault System (PFS) on Mt. Etna. The PFS is the longest and the most active on Mt. Etna: it runs for about 18 km on an approximate E-W direction in the NE flank of the volcano. At altitudes between 1000 and 1500 m a.s.l. the PFS is characterized by a near-vertical scarp max 70-80 m in height. At lower elevation (from 700-800 m a.s.l. till the Ionian Sea), the PFS is characterized by left-lateral faults with a dextral configuration. Shallow (< 2-3 km) seismic activity (2 < M < 3.5) accompanies sur-face deformation along the central and western portion of the PFS. Aseismic creep occurs on this fault as well, especially on its central and eastern portions. The motion of the PFS has been interpreted as due to the lateral spreading affecting the unstable eastern-to-southwestern sectors of Mt. Etna. Three different methodologies were used to detect radon in soil gas along the PFS. The first one consisted in Solid State Nuclear Track Detectors (SSNTD), CR-39 type, and allowed for integrated measurements. The second one consisted in spot measurements carried out with a portable device (RAD7, Durridge Company Inc.), which also allowed for thoron measurements. The last one consisted in continuous measurements by means of monitoring devices (Barasol, Al-gade) remotely placed in selected sites. The amount of radionuclides in rocks from the studied area was measured using gamma ray spectrometry. The results indicate quite the same level of radionuclides in all of the collected rock samples. Two dif-ferent horizontal profiles were investigated for soil gas radon, each consisting of ten