Spermaturia can be used as an indicator of genital and sexual maturation in puberty. In this study the mean age of the onset of puberty in Tswana schoolboys was determined. Of the boys between 10 and 13 years, only one (1.22%) aged 13 had spermaturia, compared with 61 boys (88.4%) in the group 14-16 years. The mean age of boys with spermaturia was 14.95 +/- 0.85 years. The possible onset of puberty as calculated by the presence of spermaturia was between 14.10 and 15.80 years. It would seem, therefore, that from the age of 14 years, a boy might theoretically be able to father a child. The need for sex education at school is thus of paramount importance.