Past conceptual and empirical works have identified unique differences between multiple suicide attempters, single attempters, and zero attempters, but have overlooked two distinct subgroups of single attempters: true single attempters who will not attempt suicide again, and future multiple attempters who will. Consistent with fluid vulnerability theory, the authors hypothesized that subgroups should have differences in personality traits that can predict if a first-time attempter is likely to attempt suicide again. In a sample of 127 military members (81% male, 19% female) participating in a clinical intervention study for suicidal behaviors, hypomanic symptoms—not personality traits—predicted future multiple attempters, and future multiple attempters more frequently met criteria for a bipolar-spectrum disorder. Clinical implications and convergence of findings with fluid vulnerability theory and existing research are discussed. © 2008, Wiley Periodicals, Inc. J Clin Psychol 64: 1–12, 2008.