Behavior modification applied to the treatment of obesity has evolved from the environmental control of eating behavior to a broader approach characterized by systematic manipulation of all factors associated with eating and exercise patterns. This approach has shown success in helping obese persons lose modest amounts of weight. The average length of treatment is 18 weeks, and the average weight loss is 9.9 kg. About 66% of these weight losses are maintained at 52 weeks of follow-up. Because obesity is a chronic condition with a substantial potential for relapse, longer-term treatments are needed. In the future, behavioral modification is likely to be further combined with other treatment methods.