Adipocyte fatty acid-binding protein (A-FABP) has been reported to be increased in obese adults and to be related to metabolic syndrome. Because studies concerning A-FABP in weight loss are limited and studies in obese children are missing, we analyzed A-FABP in obese children before and after weight loss. Fasting serum A-FABP, leptin, insulin, glucose, triglycerides, low-and high-density lipoprotein cholesterol, high-sensitivity C-reactive protein, and tumor necrosis factor alpha concentrations as markers of the metabolic syndrome, and weight status (body mass index and percentage body fat based on skinfold measurements) were determined in 30 obese children (median age, 11.9 years) before and after participating in a 1-year obesity intervention. Furthermore, A-FABP levels were measured in 10 nonobese children of similar age, sex, and pubertal stage. Obese children had significantly (P < .001) higher A-FABP concentrations compared with nonobese children. In backward multivariate linear regression analysis, A-FABP correlated significantly (P < .05) with percentage body fat and leptin, but not with any of the markers of the metabolic syndrome. Changes of A-FABP concentrations correlated significantly with changes of percentage body fat (r = 0.53, P = .001) and leptin (r = 0.55, P < .001), but not with any changes of parameters of the metabolic syndrome. Substantial weight loss in 10 children led to a significant (P < .05) decrease in A-FABP levels in contrast to the 20 children without change of weight status. In cross-sectional as well as longitudinal analyses, A-FABP levels were related to weight status and leptin levels. Further longitudinal studies are necessary to study the relationship between A-FABP concentrations and parameters of the metabolic syndrome.