Objective: Although research has established some relationships between risk factors and specific suicide-related outcomes, in large part the extent to which suicidal ideation and attempts have different risk profiles is unclear. Using two theories of suicidal behavior to guide our hypotheses, we studied the relationship of outwardly directed aggression to suicidal ideation and attempts in two high-risk samples. Method: Participants in Study 1 were 271 criminal offenders in a pretrial diversion program. Participants in Study 2 were 892 psychiatric inpatients who participated in the MacArthur Violence Risk Assessment Study. Results: In both studies, after controlling for relevant covariates, outwardly directed aggression was associated with suicide attempts, but not ideation. Among psychiatric patients, further analyses revealed that outwardly directed aggression was associated with planned, but not unplanned, suicide attempts. Conclusions: That aggression is related to suicide attempts and not ideation is consistent with hypotheses based on both Joiner’s (2005; Why people die by suicide. Cambridge, MA: Harvard University Press) interpersonal theory of suicidal behavior and theories based on a diathesis toward behavioral dysregulation (e.g., Mann et al., 2009). That aggression was associated with planned suicide attempts is consistent with Joiner’s theory. Competing explanations for the results include a potential role of proactive aggression in suicide attempts, particularly planned attempts. (PsycINFO Database Record (c) 2014 APA, all rights reserved)