To clarify the trend of hypercholesterolemia in Japanese adolescents, we investigated the serial changes in body mass index (BMI) and serum total cholesterol (TC) concentrations among 5,700 new students enrolled at Okayama University in 1989, 1993, and 1998. After confirming the stability of the TC assay of serum samples stored at -80 degrees C, we measured serum TC levels in stored serum samples using an automated assay system. Although serum TC levels were higher in females than in males, these levels correlated weakly and positively with BMI (r = 0.21, P < 0. 001) in males but not in females. Serum TC concentrations progressively increased from 1989-1998 in both sexes, irrespective of changes in BMI. In subjects with normal BMI (> or = 19 and < 23 kg/m2), a significant increase in serum TC was noted from 1989-1998 in both males (157.2 +/- 1.0 to 163.6 +/- 0.9 mg/dl) and females (172.0 +/- 1.1 to 175.6 +/- 1.0 mg/dl). Our results indicate on increased incidence of hypercholesterolemia even in nonobese young Japanese adolescents. A concerted effort by health and education officials together with parents is necessary to prevent a further rise in the incidence of hypercholesterolemia among young Japanese.