Patients operated on for craniopharyngioma frequently suffer from hyperphagia and are obese, but their statural growth is normal despite growth hormone (GH) deficiency. We have evaluated the hormonal factors influencing changes in weight and growth in 17 children before and 1, 3–6, 12, and/or 24 months after surgical resection of a craniopharyngioma performed at 7.7 ± (SE) 1 years of age. Of these, 15 patients had a GH deficiency before surgery, and all had complete pituitary deficiency after it. The plasma fasting insulin concentrations before surgery were positively correlated with body mass index (BMI, kg/m<sup>2</sup>; p < 0.05), plasma insulin-like growth factors (IGFI, p = 0.03, and IGFII, p = 0.04), and leptin (p = 0.03). They increased significantly 1 month after surgery and continued to increase thereafter, whereas leptin increased significantly only 3–6 months after surgery, paralleling changes in BMI. The plasma fasting insulin concentrations before surgery were also positively correlated with the weight changes (12.3 ± 2.3 kg, p < 0.01) during the 12 months after surgery, but not with changes in BMI SDS (3.1 ± 0.5, p = 0.07). Both expressions of weight change were correlated with the concomitant growth rates (4.8 ± 0.7 cm, p < 0.01). IGFI was above the 10th percentile for children with idiopathic short stature in 10 of 15 patients with craniopharyngioma-induced GH deficiency and IGF-binding protein 3 in 14 of 15 patients. Craniopharyngioma itself modified the control of insulin secretion, and surgery increased the insulin secretion which continued in the same way in a given patient after surgery. The increased insulin secretion in turn increases weight and keeps IGFI nearly normal. This may explain the normal growth rate despite the complete lack of GH.