Theoretical perspectives into suicidality have suggested that heightened perceptions of defeat and entrapment lead to suicidality. However, all previous empirical work has been cross-sectional. We provide the first longitudinal test of the theoretical predictions, in a sample of 79 students who reported suicidality. Participants completed self-report measures of suicidal ideation, depression, defeat, and entrapment at two time points, approximately 12 months apart. People higher in defeat became more suicidal over time (β =.45), with baseline levels of suicidality and depressive symptoms controlled. The current results support the posited role of perceived defeat in driving suicidal ideation. © 2011 The American Association of Suicidology.