Adiponectin is decreased in obesity and seems to be involved in insulin resistance. The influences of age, gender, puberty, and weight loss on adiponectin have not been studied in obese children. We measured body fat mass based on skinfold thickness, age, pubertal stage, gender, adiponectin, and insulin resistance (homeostasis model assessment) in 42 obese children. We analyzed adiponectin and homeostasis model assessment 1 yr later in these obese children and separated them into two groups according to degree of weight loss (decrease in sd score for body mass index, >or=0.5 vs. <0.5). Adiponectin was negatively correlated to percentage body fat (r = -0.44; P = 0.002), insulin resistance (r = -0.33; P = 0.016), and age (r = -0.41; P = 0.003). Adiponectin levels were significantly (P = 0.017) higher in pubertal girls compared with boys, but there was no significant difference in prepubertal children in respect to gender (P = 0.833). Adiponectin was significantly (P < 0.001) lower in pubertal compared with prepubertal children. The significant weight loss in 16 children was associated with a significant increase in adiponectin (P = 0.010) and a decrease in insulin resistance (P = 0.013), whereas there were no changes in the 26 children without significant weight loss. Adiponectin levels in obese children were negatively correlated to age, body fat, and insulin resistance and were decreased in puberty. Significant weight loss led to an increase in adiponectin levels and an improvement of insulin resistance.