This study explored intellectual profile of children attending a clinic for obesity and to what extent their characteristics predicted full scale IQ. Totally, 60 patients aged 8-16 years were recruited consecutively from the National Childhood Obesity Centre at Karolinska University Hospital in Sweden. These patients were tested using the Wechsler Intelligence Scale for Children (WISC). Of these 60 patients, 51 (85%) parents gave informed consent for their children's results to be included in this study (mean age 12.94, standard deviation, SD 2.42). The children's mean full scale IQ was 85.39. Parental education was strongly associated with child IQ. After adjustment for parental education, female gender and a higher level of obesity were associated with lower IQ. Obese children are at increased risk of having below average IQ and strategies to tackle associated problems should be developed in paediatric obesity clinics.