This investigation was prompted by Shuster's (1978, 1980) suggestion that acne should be regarded as a normal feature of adolescence. Acne was recorded and graded in white school children (722 boys and 788 girls) seen at approximately half-yearly intervals from age 9 to 17. Losses over the 8 years of follow-up were 16·8% for boys and 11·4% for girls. Facial acne appeared at an earlier age in girls, the prevalences being estimated to rise to a peak of 75–80% in girls aged 15–16 and 90–95% in boys aged about 17–18 years. However, the prevalence of acne at a given age depended much more upon the level of sexual maturity attained (assessed from a variety of somatic indicators) than upon age per se. On average, acne became manifest at a relatively late stage of puberty, at or shortly after peak height velocity in boys and menarche in girls. Prevalences were not affected by relative obesity nor by socioeconomic status, apparent correlations among girls disappearing when maturity status was taken into account. The proportions of subjects with moderate or severe acne increased with length of time from onset, and only about 10% showed remission during the first 3 years after onset. Acne on the body was observed in 20% of boys and 15% of girls.