Researchers have observed that attempts to suppress a thought cause either an immediate increase in the occurrence of the thought (i.e. immediate enhancement effect) or a delayed increase in the occurrence of the thought (i.e. rebound effect). In this study, we examined whether suppression of a personally-relevant, emotional thought item (i.e. a spider to spider phobics) results in an immediate enhancement or a rebound effect. Forty-eight spider phobics were randomly assigned to either a suppression group or a control group. Subjects spent three 5-min periods alone monitoring their thoughts. During the first period, subjects in both groups were instructed to 'think about anything'. During the second period, subjects in the suppression group were instructed 'not to think of a spider', whereas subjects in the control group were instructed to 'think about anything'. During the third period, subjects in both groups were instructed to 'think about anything'. The number of spider-related thoughts was recorded for each period. Results from the second period failed to support an immediate enhancement effect. Evidence for a rebound effect, however, was obtained in the third period. The theoretical and clinical implications of these findings are discussed.