Mental disorders are among the strongest predictors of suicide attempts. However, little is known regarding which disorders that are uniquely associated with suicidal behavior because of high levels of psychiatric comorbidity. We examined the unique associations between individual disorders and subsequent suicidal behavior (suicide ideation, plans and attempts) using data from the National Comorbidity Survey Replication, a nationally representative household survey of 9282 US adults. Results revealed that approximately 80% of suicide attempters in the United States have a temporally prior mental disorder. Anxiety, mood, impulse-control and substance use disorders all significantly predict subsequent suicide attempts in bivariate analyses (odds ratios (OR)=2.7-6.7); however, these associations decrease substantially in multivariate analyses controlling for comorbidity (OR=1.5-2.3) but remain statistically significant in most cases. Disaggregation of the observed effects reveals that depression predicts suicide ideation, but not suicide plans or attempts among those with ideation. Instead, disorders characterized by severe anxiety/agitation (for example, post-traumatic stress disorder) and poor impulse control (for example, conduct disorder, substance use disorders) predict which suicide ideators who go on to make a plan or attempt. These results advance understanding of the unique associations between mental disorders and different forms of suicidal behavior. Future research must further delineate the mechanisms through which people come to think about suicide and progress from suicidal thoughts to attempts.Molecular Psychiatry advance online publication, 31 March 2009; doi:10.1038/mp.2009.29.