Aims: To assess prevalence of the insulin resistance syndrome (IRS: obesity, a bnormal glucose homoeostasis, dyslipidaemia, and hypertension) in obese UK child ren and adolescents of different ethnicities and to assess whether fasting data is sufficient to identify IRS in childhood obesity. Methods: A total of 103 obes e (BMI > 95th centile) children and adolescents 2-18 years of age referred for assessment underwent an oral glucose tolerance test measurement of fasting lipid s, and blood pressure determination. Main outcome measures were prevalence of co mponents of IRS by modified WHO criteria, with IRS defined as ≥3 components (in cluding obesity). Results: There were 67 girls (65%). BMI z-score ranged from 1.65 to 6.15, with 72%having a z-score ≥3.0.Abnormal glucose homoeostasis was identified in 46%(hyperinsulinism in 40%, impaired fasting glucose in 0.8%, impaired glucose tolerance in 11 %). No subjects had silent type 2 diabetes. Dyslipidaemia was identified in 30 %and hypertension in 32%. Thirty one per cent had obesity alone, 36%had two c omponents, 28%had three, and 5%had all four components. Birth weight, BMI, and family history of IRS were not associated with risk of IRS. Higher age increase d the risk of IRS; however the syndrome was seen in 30%of children under 12 yea rs. The use of fasting glucose and insulin data for identifying IRS had a sensit ivity of 88%and specificity of 100%. Conclusions: One third of obese children and adolescents have the IRS; however type 2 diabetes is rare. Obese children wi th the IRS may form a high risk group to whom scarce intervention resources shou ld be targeted. Further work is needed to develop appropriate screening programm es for IRS components in significantly obese children. Aims: To assess prevalence of the insulin resistance syndrome (IRS: obesity, a bnormal glucose homoeostasis, dyslipidaemia, and hypertension) in obese UK child ren and adolescents of different ethnicities and to assess whether fasting data is sufficient to identify IRS in childhood obesity. Methods: A total of 103 obes e (BMI> 95th centile) children and adolescents 2-18 years of age referred for assessment underwent an oral glucose tolerance test measurement of fasting lipid s, and blood pressure determination. Main Outcome measures were prevalence of co mponents of IRS by modified WHO criteria, with IRS defined as ≥3 components (in cluding obesity). Results: There were 67 girls (65%). BMI z-score ranged from 1.65 to 6.15 with 72% having a z-score ≥3.0. Abnormal glucose homoeostasis was identified in 46% (hyperinsulinism in 40%, impaired fasting glucose in 0.8%, impaired glucose tolerance in 11%). No subjects had silent type 2 diabetes. Dyslipidaemia was identified in 30% and hyper Thirty one per cent had obesity alone, 36% had two c omponents, 28% had three, and 5% had all four components. Birth weight, BMI, and family history of IRS were not associated with risk of IRS The use of fasting glucose and insulin data for identifying IRS had a sensitvity of 88% and specificity of 100%. Conclusions : One third of obese children and adolescents have the IRS; however, type 2 diabetes is rare. Obese children wi th the IRS may form a high risk group to whom scarce intervention resources shou ld be targeted. Further work is needed to develop Appropriate screening programm es for IRS components in significantly obese children.