OBJECTIVES Many obesity-associated diseases require intensive medical treatment and are cause of a large proportion of health-related expenditures in Germany. Treatment of obesity includes nutritional, exercise and behavior therapy, usually in combination. The goal of behavior therapy for obesity is to bring about a long-term alteration in eating and exercise habits of overweight and obese individuals. Depending of the severity of obesity, drug treatment may be indicated. To evaluate the clinical and economic effectiveness of behaviour therapy for obesity considering approved drugs reducing weight, a Health Technology Assessment was carried out in the year 2008. This HTA was updated with publications up to 12/2013, along with new developments in behavior therapies and drugs. METHODS A systematic review was carried out using relevant electronic literature databases Publications chosen according to predefined criteria were evaluated by approved methodological standards of evidence-based medicine and health economics systematically and qualitatively. RESULTS Nine randomized controlled trials showed moderate but statistically significant reduction of weight in the intervention groups compared to control groups between 1.1 kg (at month 4) and 6.6 kg (at month 9). Studies with several examination time points resulted in statistically significant differences in the first evaluation time point (month 6) but not in the subsequent time points (month 12, 18, 24). The most frequent approach used for behavior therapy, was per phone or Email, two studies offered behavior therapy face-to-face. New behavior therapy approaches applied were techniques such as “Motivational Interviewing” and “Transtheoretical model”. No study was identified examining behavior therapy in combination with approved drug therapy. Two identified studies evaluating cost-effectiveness of behavior therapy per Email or phone showed cost-effectiveness for this kind of intervention but the results are biased due to a high rate of drop-outs. CONCLUSIONS Behavior therapy considering new approaches is an effective method to reduce weight.