PURPOSE: An exploratory study was done to examine the validity of the new Ballard scale with extended scoring system(eNBS) in estimating gestational age(AG) in full-term newborns. METHOD: The eNBS scoring system was extended to include all numbers of total score of NBS and GA to allow a 3-days variation in GA estimation compared to the original scale which has a 2-week variation due to the application of a 5-score interval for the total NBS score and only even numbers for GA. GA by eNBS(GA-eNBS) was compared with GA by LMP(GA-LMP) and GA by standard NBS(GA-sNBS) in 133 full-term newborns. Difference between GA-LMP and GA-eNBS was analyzed for each GA. RESULTS: Positive correlations were observed in GA-sNBS and GA-eNBS with GA-LMP. There was no difference between GA-LMP and GA-eNBS at 39GA and 40GA. At 37GA and 38GA, GA-eNBS overestimated GA-LMP up to 1 week, while underestimating up to 1 week at 41GA. CONCLUSIONS: The accuracy of eNBS was validated within 3 days of variation in GA estimation at 39-40GA. Overestimation by eNBS suggests the possible acceleration of fetal maturity in premature newborns, while underestimation, of the deceleration of fetal maturity in postterm newborns.