The secular trends in height, sitting height and leg length in Japanese children have been studied by fitting Preece-Baines Model I curves to the annual mean values from ages five to 17 of school data collected in 1957, 1967 and 1977. The method provides estimates of final adult value, and of age of maximum annual increment. Between 1957 and 1977 the maximal increments in height, sitting height and leg length all became earlier, by about a year in boys and a little less in girls. Japanese now mature about a year earlier than North Europeans. Adult height increased by 4.3 cm in boys and 2.7 cm in girls between 1957 and 1977, the increment being less in the second decade than in the first. Sitting height showed practically no increase whatever; almost the whole secular trend was due to change in leg length. Japanese now have trunk/leg proportions much more similar to those of North Europeans than was the case 20 years ago, but their adult height remains about one standard deviation lower.