The prevalence of overweight and obesity among children and adolescents has reached epidemic proportions worldwide. Among Swedish 10-year old children 15-20% are overweight and 3-5% are obese. The probability that an obese child becomes an obese adult is very high. This chronic disease requires lifetime treatment. The standard treatment of childhood obesity involves behavioural interventions focused on eating habits and physical activity. Studies often include small study samples, the absence of control groups and short treatments times. Several long-term follow-up studies of shorter interventions are available. The results from these studies are disappointing since the number of children who are "cured" i.e., have become non-obese is low. Thus, effective treatments are currently lacking.The National Childhood Obesity Center treats children in a University hospital setting. The children are enrolled from the catchment areas of the hospital as well as the rest of Sweden. Treatment alternatives include behavioural treatment (individual and group), low and very low calorie diet, pharmacological and surgical treatment. Patients treated with surgical and pharmacological methods safety is ensured using these treatments exclusively in controlled studies. The clinic was the first in Sweden with this wide range of treatment options.

BORIS is a national health care quality register for childhood obesity, supervised by the Swedish Association of Local Authority and Regions.

The primary aim of this study was to compare treatment effects (changes in BMI SDS) during the first three years of behavioral treatment in relation to age at start of treatment. The secondary aim was to evaluate specific factors of importance (gender, heredity, parental weight status, socioeconomic factors and age at obesity onset) for treatment effects. The third aim was to investigate factors correlated to drop out.

This is a longitudinal study of all patients referred to National Childhood Obesity Center between January 1997 and December 2004. Only patients with behavioral treatment were included. Patients with other treatments (VLCD/LCD, drugs and surgery) and other diagnoses (syndromes, craniopharyngioma, Mb Down, myelomeningocele, various types of mental and psychological disorders) and children <6 and >17 year at inclusion were excluded. The remaining children were divided into three age groups of obese children depending of age at onset of obesity treatment (6-9, 10-13 and 14-16year). All patient data were registered in the BORIS nationwide childhood obesity database.

Inclusion Criteria:

• All children treated with behavioral treatment at the National childhood obesity center Stockholm between january 1998 - december 2004.
• Classified as obese by using the Tim Cole standard.

Exclusion Criteria:

• Children with obesity together with other diagnosis
• Children with other treatment like pharmacological, low calorie diets and surgery