A possible relationship between Joiner's (2005) interpersonal-psychological theory of suicidal behavior and optimism was investigated by examining the ability of optimism to act as a moderator of perceived burdensomeness, thwarted belongingness, and acquired capability to engage in self-injury in the prediction of suicidal ideation. Results supported hypotheses that optimism would serve as a moderator of the effects of thwarted belongingness and perceived burdensomeness in the prediction of suicidal ideation; however, similar results were not found regarding the acquired capability to engage in self-injury. How optimism might play a role in alleviating suicidal ideation and clinical implications of the findings are discussed.