Gamma-glutamyl transferase (GGT) is a marker for cardiovascular risk and an independent predictor of long-term outcome in adults. Epidemiological data from pediatric cohorts are rare. We studied the association of GGT to body mass index as a standard deviation score, sex, and age in 68,415 children (age 11.7 ± 4.4 years; 48% boys; body mass index 27.2 ± 7.4 kg/m2; GGT measured in n = 23,955). GGT >50 U/L is strongly associated with extreme obesity (odds ratio 27.13, 95% confidence interval 15.07-48.85) and male sex (odds ratio 2.60, 95% confidence interval 2.03-3.31). GGT seems to be of clinical relevance and may be marketable as a surrogate in risk profiling for children with obesity.