The current Italian seismic catalogues are generally considered «complete» as regards the destructive seismic events which occurred from the 17th century onwards. In fact, research performed using target methodologies still reveal earthquakes of high intensity, not yet known to the seismological tradition. This is the case of an earthquake which occurred on 14 September 1780, which caused serious damage and victims in some towns of the Tyrrhenian coast of North-eastern Sicily (Io = VIII MCS). The information reported in an anonymous printed account was verified in the administrative records; this allowed a reconstruction of a macroseismic outline of great interest, which may make more precise the seismic hazard assessment in an area at high environmental risk due to the presence in Milazzo of an important chemico-industrial complex.