Accurate prediction of weight loss success and failure has eluded researchers for many years. Thus, we administered a comprehensive psychometric battery before a 4-month lifestyle behavioral weight reduction program and analyzed weight changes during that period to identify baseline characteristics of successful and unsuccessful participants, among 112 overweight and obese middle-aged women (age, 47.8 +/- 4.4 years; BMI, 31.4 +/- 3.9 kg/m2). Mean weight and percentage fat losses among the 89 completers were -5.4 kg and -3.4%, respectively (p < .001). A higher number of recent dieting attempts and recent weight loss, more stringent weight outcome evaluations, a higher perceived negative impact of weight on quality of life, lower self-motivation, higher body size dissatisfaction, and lower self-esteem were associated with less weight loss and significantly distinguished responders from nonresponders among all participants. These findings are discussed as to their usefulness (i) to screen individuals before treatment, (ii) to provide a better match between interventions to participants, and (iii) to build a weight loss readiness questionnaire.