Terror management theory argues that mortality-induced terror motivates group identification. Uncertainty-identity theory argues that uncertainty about what happens after death motivates group identification. Two experiments were conducted to test the latter reasoning. In Experiment 1 (n=187), mortality salience was manipulated, and uncertainty about the afterlife was measured to predict national identification. As hypothesized, mortality salience strengthened identification only among those who were uncertain about the afterlife. In Experiment 2 (n=177), mortality salience was manipulated as before, but belief in an afterlife was also manipulated-participants were primed to believe that there was an afterlife, there was not an afterlife, or the existence of an afterlife was uncertain. As in Experiment 1, mortality salience strengthened identification only among those who were existentially uncertain. These experiments show that uncertainty plays a significant role in reactions to mortality salience, and support uncertainty-identity theory's analysis of the role of self-uncertainty in ideological conviction and group behavior.