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The aim was to study secular changes in head dimensions of Japanese adult males. The subjects were all of Japanese birth and Japanese ancestry. The age range of the subjects was between 18 and 25 years. Four head measurements were taken: head length, head breadth, head height and head circumference. In addition, stature and body weight were also measured. All measurements were made by one observer (Fumio Ohtsuki) from 1998 to 2001. The present sample was compared with the series taken between 1910 and 1917 of Matsumura (J Fak Sci Imp Univ Tokyo Sec 1 (1925) 1) and the one measured in 1965 of Morita and Ohtsuki (Hum Biol 45 (1973) 151). The present study demonstrated the presence of larger means for head length, head breadth and cephalic index in the current sample than in their predecessors of about 35-85 years ago. Also, the present series displayed larger head circumference than that of the Morita and Ohtsuki series. Using ANOVA, head length and head breath showed significant (p<0.01) differences among all birth-year cohorts from 1978 to 1983 of the current sample. Head height, head circumference and cephalic index did not display significant differences. However, the slope of the regression line indicated that all measurements as well as the cephalic index showed slightly decreasing tendencies during the investigated period. These results suggest that brachycephalization has been occurring for approximately about 35-85 years in adult Japanese males, but the change seems to have become reversed slightly during the period covered by the present sample.