Auxological data have been used to monitor the health of individuals and also the health of populations since 1833. The two uses are distinct, both in theory and in methods used, and should not be confounded, as they so often are at present. Some results of population monitoring in Holland, Cuba and the UK are described; in the UK an effective population surveillance system covering ages 0–11 has been operative since 1972. In comparing populations, the distinction between tempo of growth and ultimate size has to be observed; Japanese boys aged 13 and 14 are as tall as British boys, but Japanese 19-year-olds are 5 cm shorter. In monitoring individuals, velocity or incremental standards are much more effective than ‘distance’ standards, and tempo-conditional standards are essential over the age of 9.