Objective: While in adults not total body- or visceral fat mass, but liver fat content was found to independently determine insulin resistance, it is unclear whether these relationships are already present in obese adolescents. Design and Methods: 39 overweight/ obese adolescents were matched for sex and BMI with 39 adults. To compare the age- and sex-specific BMI values of adolescents and adults, the percentile value of each adolescent was projected to the age of 18. Body fat depots were quantified by whole-body magnetic resonance (MR) imaging. Liver fat content was measured with (1) H-MR spectroscopy. Insulin resistance was estimated from the homeostasis model assessment of insulin resistance (HOMA-IR). Results: Compared to overweight and obese adults, adolescents had higher HOMA-IR (p<0.001) and lower lean body mass (p=0.002). Furthermore, they had higher total body- (p=0.02), but lower visceral- (p<0.001) fat mass, while liver fat content was not significantly different between the groups (p=0.16). In both groups liver fat content (both p≤0.007), but not total body- or visceral fat mass (all p≥0.64) was an independent predictor of insulin resistance. Conclusions: Having lower visceral fat mass, overweight and obese adolescents are more insulin resistant than sex- and BMI-matched adults. Liver fat content, but not total body- or visceral fat mass, is an independent determinant of insulin resistance in adolescents.