Suicide is a leading cause of death that is difficult to predict because clinical assessment has relied almost exclusively on individuals' self-report of suicidal thoughts. This is problematic because there often is motivation to conceal such thoughts. The authors tested the ability of the Self-Injury Implicit Association Test (SI-IAT), a reaction-time measure of implicit associations between self-injury and oneself, to detect and predict suicide ideation and attempts. Participants were adolescents who were nonsuicidal (n = 38), suicide ideators (n = 37), or recent suicide attempters (n = 14). Analyses revealed large between-group differences on the SI-IAT, with nonsuicidal adolescents showing large negative associations between self-injury and themselves, suicide ideators showing small positive associations, and suicide attempters showing large positive associations on this performance-based test. The SI-IAT accurately predicted current suicide ideation and attempt status as well as future suicide ideation, and it incrementally improved prediction of these outcomes above and beyond the use of known risk factors. Future research is needed to refine this assessment method and to further develop and examine performance-based assessment of suicide risk in clinical settings.