The main purpose of this prospective intervention study was to determine whether eating styles after an intensive, partly inpatient, one year combined lifestyle intervention are associated with weight change in the following year in severely obese children and adolescents.A total of 120 participants (8-19 years) with an average SDS-BMI of 3.41 (SD = 0.38) was included. Measurements were conducted at baseline (T0), at the end of treatment (T12) and at the end of follow up two years after baseline (T24). The primary outcome measurement was the δSDS-BMI between T12 and T24. As primary determinant of weight change after treatment, the participants eating styles were evaluated with the Dutch Eating Behavior Questionnaire - child report that measures external, emotional and restraint eating. The association between outcome and determinant was assessed in linear regression analyses. Complete data were available for 76 of the 120 participants.This study shows that for girls a higher score on restraint eating at T12 and a higher score on external eating at T12 were associated with more weight (re)gain in the year after treatment. No statistically significant association with emotional eating at T12 was found. In addition for girls a higher score on external eating at T0 was associated with more weight (re)gain in the year after treatment. Furthermore, the observed changes in eating styles suggest that on average it is possible to influence these with treatment, although the detected changes were different for girls and boys and for the different eating styles.More generally, this study indicates that for girls the levels of restraint and external eating after treatment were associated with the weight change during the following year. Trial registration: : Netherlands Trial Register (NTR1678, registered 20-Feb-2009).