Background: Bariatric surgery candidates have higher rates of co-morbid psychological illnesses than those in the general population. The effect of weight loss on these illnesses is unclear. Methods: This prospective observational study explored psychiatric co-morbidities and weight loss outcomes in 204 gastric banding surgery candidates. Psychiatric co-morbidities were assessed prior to surgery and 2 years post-surgery. One hundred and fifty patients (74 ) completed assessments at both time points. Results: At baseline, 39.7 of the patients met the criteria for a current axis I disorder as defined by the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV). Mood disorders were the most frequent (26.5 ), followed by anxiety disorders (15.2 ) and binge eating disorder (13.2 ). Preoperative psychopathology predicted clinical psychopathology at 2 years. No preoperative or post-operative axis I disorder was significantly related to weight loss at 2 years. The frequency of current axis I disorders decreased significantly from 39.7 preoperatively to 20 2 years post-surgery. Conclusions: The point prevalence of psychopathology in this sample of Australian bariatric candidates is high. Psychopathology, preoperatively and at 2 years of follow-up, was not associated with weight loss at 2 years. ? 2014 Springer Science+Business Media New York.