Background: Although treatment failure after Vertical Banded Gastroplasty (VBG) is not uncommon, the safety of the procedure makes it the most widely used form of bariatric surgery, The reasons for failure may be either technical, such as staple-line dehiscence, or psychological inability on the part of the patient to adjust to the small stomach pouch and to its consequences. Methods: We carried out prospective testing of a cohort of consecutive VBG candidates, using a battery of psychological tests consisting of the 'Three Factor Eating Questionnaire', 'Hopkins Symptom Check List (HSCL)', 'Mood Adjective Check List (MACL)', 'Karolinska Scales of Personality (KSP)', and two projective tests, the 'Meta-Contrast Technique (MCT)' and the 'Perceptgenetic Object Relation Test (PORT)'. The patients had been scheduled for surgery on clinical considerations only, and the results of the psychological testing were not disclosed to the surgeons until after the follow-up. Results: Mean preoperative Body Mass Index (BMI) was 42.0 (SD 9.9). Patients were extensively tested during the 3 weeks prior to surgery. There were no operative complications. Patients were tested psychologically again after 3 years. Their mean BMI then was 32.3 (SD 5.6). Thirteen patients had lost more than 50% of their overweight (BMI mean 29.6; sc 1.1), seven patients had lost less than 50% (BMI mean 37.0; SD 1.6; p=0.0043). These two groups were compared. The single factor that correlated consistently with an unsatisfactory weight loss was preoperative signs of depression (p=0.04). Stepwise discriminant analysis using three preoperative factors (Hunger, Verbal aggression and Socialization) correctly classified 90% of the patients who had lost <50% of their overweight. Other variables (Impulsivity, Emotional detachment and Maladaptive psychological defence) identified patients who were later to suffer from dysphoric mood (n=5) or disturbed eating behaviour (n=11). These factors may compromise a sustained ability to tolerate food restriction. Despite the operation's disadvantages, all patients considered it worthwhile and displayed improved psychosocial adaptation postoperatively. Conclusion: We conclude that extensive psychological testing can accurately predict the intermediate-term weight outcome following VBG and that even patients who show little weight loss benefit from the procedure.