Objective: Assess the incidence and determinants of hospitalization for deliberate self-harm and mental health disorders, and suicide after bariatric surgery. Background: Limited recent literature suggests an increase in deliberate self-harm following bariatric surgery. Methods: A state-wide, population-based, self-matched, longitudinal cohort study over a 5-year period between 2007 and 2011. Utilizing the Western Australian Department of Health Data Linkage Unit records, all patients undergoing bariatric surgery (n = 12062) in Western Australia were followed for an average 30.4 months preoperatively and 40.6 months postoperatively. Results: There were 110 patients (0.9%) hospitalized for deliberate self-harm, which was higher than the general population [incidence rate ratio (IRR) 1.47, 95% confidence interval (CI) 1.11-1.94, P = 0.005]. Compared with before surgery, there was no significant increase in deliberate self-harm hospitalizations (IRR 0.79, 95% CI 0.54-1.16; P = 0.206) and a reduction in overall mental illness related hospitalizations (IRR 0.76, 95% CI 0.63-0.91; P = 0.002) after surgery. Younger age, no private-health insurance cover, a history of hospitalizations due to depression before surgery, and gastrointestinal complications after surgery were predictors for deliberate self-harm hospitalizations after bariatric surgery. Three suicides occurred during the follow-up period, a rate comparable to the general population during the same time period (IRR 0.61, 95% CI 0.11-2.27, P = 0.444). Conclusions: Hospitalization for deliberate self-harm in bariatric patients was more common than the general population, but an increased incidence of deliberate self-harm after bariatric surgery was not observed. Hospitalization for depression before surgery and major postoperative gastrointestinal complications after bariatric surgery are potentially modifiable risk factors for deliberate self-harm after bariatric surgery.