OBJECTIVE: To assess the effectiveness of an evidence -based treatment of obesity in a primary care setting, we conducted the S.A.T.-trial (Sibutramine in Adiposity Trial) which is a multicentre, double-blind, placebo-controlled, randomised parallel group comparison of a 54 weeks continuous therapy with Sibutramine 15 mg or Placebo in addition to a standardised non-pharmacological therapy consisting of a calorie-restricted diet, modification of eating behaviour and lifestyle, and an activity programme. Patients with a BMI of >30 and less than 40 are included. The primary endpoint in this study is weight loss in kg between the last measurement of body weight (visit 11) and the measurement at the first visit. Secondary endpoints are amongst other clinical parameters health economic and quality of life data. METHODS: Quality of life is measured by 4 different instruments: the Short Form 36 (SF-36): the EuroQol, the Time-trade-off-Method (TTO) and the Willingness-to-pay-Method (WTP).The SF-36 is a general, standardised and validated Quality-of-life-instrument, consisting of 36 questions which can be aggregated into 8 health dimensions. The EuroQol is also a general, standardised and validated quality-of-life-questionnaire, having the advantage of aggregating the five health dimensions into one quality-of-life-index. Therefore, the EuroQol is frequently used in health economic evaluations to calculate Quality adjusted life years saved (QALYs).In the TTO-Interview patients are asked questions to calculate a quality-of-life-index for each patient stratified by age. In the willingness-to-pay-questionnaire, obese patients are asked how much they would be prepared to pay per month for an immediate and sustained weight loss of 10 kg from their current body weight. The answers are stratified by net income classes. RESULTS: Quality of life measured by the SF 36 has improved in all 8 health dimensions at visit 2 compared to visit 1. Especially social functioning is impaired in obese patients. The quality-of-life-index measured by the EuroQol has slightly improved from visit 1 to visit 2 over all age-groups. The quality-of-life-index of the TTO-interview and the EuroQol-questionnaire are very similar except for the age group <35 years. Willingness-to-pay correlates positively with net income. DISCUSSION: The results reveal the massive burden of obese patients.