The aim of this study was to compare the prevalence and pattern of metabolic syndrome in children and adolescents in the interval between the Korean National Health and Nutrition Examination Surveys (KNHANES) in 1998 and 2001. Two nationwide surveys (KNHANES) were conducted in Korea in 1998 and 2001. A stratified multistage probability sampling design was used to ensure representation of the entire Korean population. The National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATP III)-derived definition was used for the definition of metabolic syndrome. A total of 1763 (mean age+/-SD of 14.6+/-2.8 yr) and 1245 (14.1+/-2.8 yr) Korean children and adolescents in the age range 10-19 yr participated in the studies of 1998 and 2001, respectively. The prevalence of metabolic syndrome in male children and adolescents increased significantly from 5.7% in 1998 to 9.0% in 2001. However, there was no increase in females (5.1% in 1998 and 4.9% in 2001). Of the 5 components of metabolic syndrome, low HDL-cholesterolemia showed the highest increase in males and females during the 3 yr. Hypertriglyceridemia increased next in both genders. In contrast, the proportion of female subjects meeting the fasting glucose criterion decreased over the same period. As dyslipidemia was the principal contributor to the increase in metabolic syndrome in Korean male children and adolescents during the 3 yr, a strategy of dietary pattern change and the encouragement of physical activity should be introduced to these groups at a national level.