There are few long-term studies on suicide in psychiatric settings in China. The objective of this study was to evaluate the long term suicide risk and its associated factors after the initial psychiatric assessment. Demographic and clinical data of adult subjects receiving psychiatric assessment between 1996 and 2000 in a district hospital in Hong Kong were retrieved from the hospital computer system. Data were matched with completed suicides before June 30 2015 as recorded by the Coroner's Office. From a total of 4078 subjects identified, there were 152 (3.7%) recorded suicides; one-fifth of suicides occurred within one year, and half within 5 years. Cox regression analysis revealed that the risk of suicide after the initial psychiatric assessment was positively associated with deliberate self-harm (Hazard ratio = 2.1; 95%CI = 1.5–3.0; p < 0.001), and negatively associated with ‘no psychiatric disorder’ (Hazard ratio = 0.4; 95%CI = 0.2–0.6; p = 0.001). The overall suicide risk for those diagnosed to have a psychiatric disorder was 4.4%; 4.5% for men and 4.3% for women. Deliberate self-harm and having a psychiatric disorder at the time of assessment are significant risk factors of suicide. Appropriate treatment of psychiatric disorders and comprehensive management of deliberate self-harm are important for suicide prevention.