OBJECTIVE. Studies among patients have shown accelerated weight gain after (adeno)tonsillectomy.* Whether (adeno)tonsillectomy is also a risk factor for the development of overweight is unknown. We investigated the association between (adeno)tonsillectomy and the subsequent development of overweight in the general population. METHODS. The study population consisted of 3963 children participating in the Dutch Prevention and Incidence of Asthma and Mite Allergy birth cohort. Data on weight and height, adenoidectomy and tonsillectomy, and covariates (gender, birth weight, maternal education, maternal overweight, maternal smoking during pregnancy, breastfeeding, and smoking in the home) were obtained from annual questionnaires completed by the parents. In addition to the questionnaire data, weight and height were measured by the investigators when the children were 8 years old. RESULTS. (Adeno)tonsillectomy between 0 and 7 years of age was significantly associated with overweight and obesity at age 8. Overweight at the age of 2 years was not associated with increased risk of (adeno)tonsillectomy in later years, indicating that the association between (adeno)tonsillectomy and overweight was not explained by preexisting overweight. Longitudinal data on weight and height in the years before and after surgery suggest that (adeno)tonsillectomy forms a turning point between a period of growth faltering and a period of catch-up growth, which might explain the increased risk to develop overweight after the operation. CONCLUSION. Children who undergo (adeno)tonsillectomy are at increased risk to develop overweight in the years after surgery.