The age-related evolution of serum cholesterol has been studied in a cohort of 475 boys and girls born in 1964, living in Berlin-Pankow district; they have been followed up from age 13-14 to 20-21 (response rate after eight years: 66%). At age 13-14, mean total cholesterol was higher among boys (183 +/- 34 mg/dl) as well as among girls (187 +/- 33 mg/dl) as compared with those observed in other populations. About one third of the subjects at this age had values greater than 200 mn/dl. There was a marked decrease in mean total cholesterol around age 14 in both sexes, inversely related to the degree of sexual maturity. Between age 15 and 20 the serum cholesterol rose continuously. After puberty girls had higher mean values than boys. The evolution of serum cholesterol changes during adolescence should be taken into account when assessing preventive measures in children and young people.