It is a consistent finding that, among obese patients, the weight lost as a result of the most widely available treatments for obesity is almost always regained. This relapse appears to be attributable to the individual's inability to persist with the behavioural strategies needed to maintain the new lower weight. Little research has investigated the psychological mechanisms that might account for this phenomenon. This study aimed to identify psychological factors that predict weight regain. Fifty-four women with obesity who had lost weight by attending community slimming clubs were interviewed immediately after losing 10% of their initial body weight, and then followed-up every 2 months for a period of 1 year by means of telephone interviews. The results identified two prospective predictors of weight regain: one cognitive factor (dichotomous thinking) and one historical variable (maximum lifetime weight). The finding that a specific cognitive style is a significant predictor of relapse has implications for the treatment of obesity.