Self-efficacy is an important predictor of treatment outcomes for a variety of addictive behaviors. However, little research is available regarding its predictive value in obesity treatment. We assessed the predictive validity of the 20-item version of the Weight Efficacy Lifestyle Questionnaire (WEL) in a consecutive sample of 109 obese adults seeking outpatient treatment at a university-based weight-management center. Although the WEL demonstrated a stable factor structure and sound psychometric properties, it failed to correlate with either program attendance or weight loss. We concluded that self-efficacy judgments (as measured by the WEL) are not predictive of short-term obesity treatment outcomes.