The relationship between maternal smoking and the head circumference of newborns were analyzed using a matched-pair longitudinal method. For the study, data was collected from Japanese primiparas in Aichi, Japan. Forty-seven smoking and nonsmoking mothers were matched using multivariate caliper matching for birth weight and gender for their newborns, and gestational period and age for the gravidas. Significantly smaller head circumferences of the newborns from the smoking mothers were observed.