Abstract: A paleodemographic analysis was conducted using skeletal data from Jōmon period sites in Japan. 15P5 ratios were produced as proxy birth rate values for sites throughout the Jōmon period. Previous studies based on numbers of residential sites indicated a substantial population increase in the Kantō and Chūbu regions in central Japan, climaxing during the Middle Jōmon period, followed by an equally dramatic population decrease, somewhat resembling changes that occurred during a Neolithic Demographic Transition (NDT). The Jōmon are viewed as a relatively sedentary, non-agricultural group, and provided an opportunity to attempt to separate the factors of sedentism and agriculture as they relate to the NDT. Skeletal data showed fairly stable trends in birth rates, instead of the expected increase and decrease in values. This discrepancy calls into question the validity of previous studies. The stable population levels suggest that sedentism alone was not the primary driver of the NDT.