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Micro-tectonic deformations have been monitored continuously in 3D in Postojna Cave, Slovenia with TM 71 extensometers since 2004. Two instruments, 260 m apart, were installed on the Dinaric oriented (NW-SE) fault zone that is situated about 1,000 m north of the inner zone of the regionally important Predjama Fault. Monitoring on both instruments has shown small tectonic movements (ie, a general dextral horizontal movement of 0.05 mm in four years [Postojna 1] and extension of 0.03 mm in four years [Postojna 2]). Between the longer or shorter calm periods, eleven extremes have been recorded regarding characteristic changes in displacement. The largest short-term movement was a compression of 0.04 mm in seven days, detected in March 2005, which coincided with the 25 km distant Ilirska Bistrica earthquake (ML 5 3.9). About two months before the earthquake an extension of 0.05 mm occurred and one month before the earthquake the strain changed into a compression of 0.05 mm. The largest permanent peak was detected at the end of 2004. Along the y-axis (Postojna 1) there was a dextral horizontal movement of 0.075 mm in one month (November 10 to December 15, 2004). After the sinistral horizontal movement of 0.02 mm (December 15–27, 2004), the y-axis retained its permanent position on 0.05 mm, where it remained for more than a year. Regarding the extremes, ten earthquakes were selected that coincided with tectonic micro-displacements. In terms of speleogenesis, the monitored fault zone represents a stable cave environment. Because radon flux is known to change significantly during tectonic and seismic activities …