The aim of the present study was to determine the change of serum uric acid (UA) levels in male adolescents and to characterize the relationship between UA levels and obesity or its related factors. This study was conducted in 17,155 students at enrollment in Okayama University from 1991 through 2002, in which the mean serum UA level as a whole was 5.64 +/- 0.009 mg/dL (mean +/- SEM) and the incidence of hyperuricemia (>/=7.6 mg/dL) was 4.13%. Serum UA levels were correlated with obesity-related indicators, including body mass index (BMI; r = 0.282, P <.0001) and skin-fold thickness (r = 0.286, P <.0001). The incidence of hyperuricemia was increased in parallel with BMI. In the last 4 years (1999 through 2002) of the study period, serum UA levels (5.76 mg/dL) and the incidence of hyperuricemia (4.5%) were significantly increased compared with those in the earlier period (1991 through 1994: 5.50 mg/dL and 3.5%, respectively). However, BMI has been rather gradually decreased throughout 12-year observation in all the subjects. Hyperuricemia was related to the presence of other risk factors, including hypercholesterolemia, liver function abnormality, and hypertension. The frequencies of such abnormalities were higher than euuricemic subjects and this trend was notable in the most recent students enrolled from 1999 through 2002. Hyperuricemia was even found in the group of non-obese male adolescents. Taking into consideration that hyperuricemia is associated with a high prevalence of lifestyle-related diseases in adults, it is of great importance to prevent hyperuricemia at the early stage in Japanese adolescents.