OBJECTIVE The skin color of newborn infants is subjectively observed to change, depending upon their gestational age. We evaluated the relationship between neonatal skin color and gestational age by employing an objective method. METHODS Using a tristimulus photocolorimeter, L*, a*, and b* were examined as the parameters of skin color in Japanese newborn infants (Commission Internationale de l'Eclairage L*a*b* color space). The following items were examined: (1) the reproducibility of the measurements; (2) the time course of the values during the first 24 h after birth, and (3) the relationship with the gestational age. The gestational age of these infants had been determined by measuring their crown-rump length during fetal periods. RESULTS Reliability and validity of the measurements were satisfactory for all parameters. However, a* and b* fluctuated widely during the first 24 h. By contrast, L* was stable between 3 and 24 h after birth. L* measured during these periods directly correlated with the gestational age (r=0.843, p<0.0001). CONCLUSIONS Because L* represents lightness or darkness, our results suggest that the skin color changes from black to white with maturation. L* may be a helpful parameter for the evaluation of the gestational age of newborn infants.