PURPOSE: The purpose of this study was to standardize the somatosensory evoked potential (SEP) latency and amplitude of healthy preterm infants according to the postconceptional age. METHODS: The median nerve SEPs were recorded in 30 healthy preterm infants who were followed up until 6 months and were neurodevelopmentally normal. RESULTS: The mean peak latency and interpeak amplitude were following : P0=20.89+/-6.09 (msec), N1=26.32+/-5.18, P1=31.16+/-6.59, N2=36.52+/-7.22 : P0N1=1.07+/-0.72 (microvolt), N1P1= 1.56+/-0.93, P1N2=1.56+/-1.73. The N1 peak latency was inversely related to post- conceptional age. (P=0.036) : below 36 weeks=29.44+/-3.18 (msec), from 36 weeks to 37+6 weeks=27.72+/-5.47, from 38 weeks to 39+6 weeks=25.20+/-5.86, above 40 weeks=22.70+/-2.09. CONCLUSION: This study demonstrates normal ranges of SEP of median nerve in preterm infants as a basic data of neurodevelopmental prognostic assessment.