Objective: Hospital treated deliberate self-poisoning is common in young people. Internationally, estimates of rates of depression in this population are very wide (14.6% to 88%). The aims of this study were to determine the prevalence of depression and the independent predictors of referral for psychiatric hospitalisation in young people (aged 16 to 25 years) following an index episode of hospital treated deliberate self-poisoning. Method: A retrospective cohort study design (n = 1410), with data drawn from a population-based clinical case register. Unadjusted and adjusted estimates of predictors of referral for psychiatric admission (after-care) used logistic regression models. Results: Prevalence of any depression diagnosis was 35.5% (n = 500); and 25.4% (n = 358) were referred for a psychiatric admission. The adjusted estimates for predictors of psychiatric inpatient referral were: high suicidal level (OR 118.21: CI 95% 63.23–220.99), low/moderate suicidal level (14.27: 9.38–21.72), any depression (2.88: 1.97–4.22), any psychosis (4.06; 1.15–14.36), older age (1.12: 1.04–1.21), and number of support people (0.88: 0.78–0.98). Conclusion: Depression was diagnosed in more than a third and was an independent predictor of psychiatric inpatient referral, so service providers need to account for this level of need in the provision of assessment and after-care services. Evidence-based guidelines for psychiatric inpatient after-care for deliberate self-poisoning and/or depression in young people are limited. Our explanatory model included suicidal level, depression, psychosis, older age, and available support persons, suggesting that the treating clinicians were making these discharge decisions for admission in keeping with those limited guidelines, although the balance of benefits and harms of psychiatric hospitalisation are not established. Future research examining patient experiences, effectiveness of psychiatric hospitalisation, and alternatives to hospitalisation is warranted.