The purpose of this study was to clarify the relationship between lower birth weight and current overweight status and to examine the involvement of these factors in the development of the metabolic syndrome (MS) in obese Japanese children. We examined 97 obese boys (mean age 11.3 years; mean percentage overweight [POW] 52.4%) and 29 obese girls (mean age 11.1 years; mean POW 58.3%). The anthropometric measurements, blood pressure, fasting serum insulin and blood glucose, liver enzymes, lipids and lipoproteins were measured. Birth weight and gestational weeks were also recorded. The subjects were divided into either an MS group or a Non-MS group using criteria proposed for Japanese children. We compared the weight parameters (birth weight, current weight and current weight-to-birth weight ratio [WBWR]) between the two groups and analyzed the relationships between the weight parameters and metabolic derangements. There were no significant differences in age or anthropometric measurements between the two groups. However, birth weight in the MS group was lower than that in the Non-MS group, while WBWR of the MS group was higher than that in the Non-MS group. Blood pressure and serum insulin correlated positively with WBWR. These findings suggested that lower birth weight with current overweight status was associated with the MS in obese Japanese children. We were unable to clarify whether subjects with lower birth weight who achieved proper weight gains had the same risk as subjects with appropriate birth weight. However, they should be assisted to grow adequately to prevent future metabolic derangements.