Drawing from self-affirmation theory (C. M. Steele, 1988) and L. L. Martin and A. Tesser's (1989, 1996) theory of ruminative thinking, the authors hypothesized that people stop ruminating about a frustrated goal when they can affirm an important aspect of the self. In 3 experiments participants were given failure feedback on an alleged IQ test. Failure feedback led to increased rumination (i.e., accessibility of goal-related thoughts) compared with no-failure conditions (Studies 1 and 2). Rumination was reduced when participants could self-affirm after failure (Studies 1 and 2) or before failure (Study 3). In Study 3, self-affirmation led to increased positive affect on a disguised mood test and more positive name letter evaluations. Moreover, the obtained increase in positive affect mediated the effect of self-affirmation on rumination. It is concluded that self-affirmation may be an effective way to stop ruminative thinking.