To evaluate (1) the pattern of post-operative weight gain and (2) the risk factors associated with the development of post-operative weight gain and obesity in children treated for craniopharyngioma.The records of 43 children who had primary craniopharyngioma resection were reviewed. Neurological, endocrine, anthropometric and radiological risk factors for the development of obesity and for post-operative increase in BMI SDS were analyzed.Twenty-five patients (58%) became obese post-operatively. Obesity was significantly associated with higher BMI SDS at presentation and pre-operative hydrocephalus (p < 0.05). Increased BMI SDS from 0-12 months was significantly associated with post-operative MRI evidenced hypothalamic damage and higher BMI at presentation (p < 0.05).Children who developed hypothalamic obesity had a significant, rapid BMI increase over the first 6 months, followed by stabilization, with no regression of BMI SDS.