Objective  Childhood obesity is increasingly common and is associated with health problems; in particular, obesity plays a central role in the metabolic syndrome (MS). We estimated the prevalence of MS in Caucasian children and adolescents with varying degrees of obesity.

Patients and methods  We studied 191 obese [body mass index (BMI) > 97th percentile] children and adolescents. Obesity was stratified on the basis of a threshold BMI z-score and subjects were classified as moderately (z-score 2–2·5) or severely obese (z-score > 2·5). Seventy-six, nonobese subjects were recruited into a comparison group. Thirty-one of them were of normal weight (BMI < 75th percentile) and 45 overweight (BMI 75th–97th percentile).

Patients were classified as having MS if they met three or more of the following criteria for age and sex: BMI > 97th percentile, triglyceride levels > 95th percentile, high density lipoprotein (HDL) cholesterol level < 5th percentile, systolic or diastolic blood pressure > 95th percentile and impaired glucose tolerance (blood glucose level: 7·8–11·1 mmol/l at 2 h). Insulin resistance was calculated using the homeostasis model assessment for insulin resistance (HOMA-IR) and impaired insulin sensitivity was defined as a HOMA-IR ≥ 2·5 in prepubertal patients and HOMA-IR > 4 in pubertal subjects.

Results  The overall prevalence of MS was 13·9% and was present in 12·0% of moderately obese and 31·1% of severely obese subjects; no overweight or normal weight subjects met the criteria for MS. The rate of the MS increased progressively with increasing BMI categories (P < 0·001). Severely obese patients had a threefold increased risk with respect to moderately obese patients.

Conclusions  The prevalence of the MS is higher in obese as opposed to nonobese subjects and increases with severity of obesity.