this paper presents the percentage distribution of the body mass index of the brazilian population from birth to age 25, based on a national survey conducted in 1989. survey data show that body mass index decreases from birth until around 6 years of age, reaching a plateau at 8 years and progressively increasing until the age of 19 or 20 years for females and 20 or 21 for males. the survey also revealed that after the age of 12 females present a greater body mass index than males, as well as a larger range of percentile values (from 3 to 97). a comparison with data from other countries showed that the body mass index profile in brazil is similar to that observed in france, great britain, and the united states. before the age of 6, brazilian youngsters have a mean body mass index that resembles that of north american children, and a lower one thereafter. a comparison between the median body mass index of brazilian and british youngsters revealed consistently lower values among brazilian females. when compared to that of france, brazil's male population has a systematically lower body mass index after the age of 8. it is suggested that the data presented in our study be used only for comparing groups of individuals and studies, and not for screening or clinical monitoring, due to the great variability in growth patterns during adolescence.