The number of fluctuations of skin conductance per second correlates with postoperative pain. The aim of this prospective study was to test the cut-off value for the number of fluctuations of skin conductance per second obtained from a previous study. Seventy-five patients were asked to quantify their level of pain on a numeric rating scale (0-10) in the recovery room. The number of fluctuations of skin conductance per second was recorded simultaneously. The number of fluctuations of skin conductance per second was different between patients with no (0.07), mild (0.16), moderate (0.28) and severe pain (0.33); p < 0.001. The tested cut-off value for the number of fluctuations of skin conductance per second (0.1) distinguished a numeric rating scale </= 3 from > 3 with 88.5% sensitivity and 67.7% specificity. The number of fluctuations of skin conductance per second may be a useful means of assessing postoperative pain.