Intrusive thoughts (e.g., anxiety, depression, substance use) are among the most salient symptoms of clinical problems. Therefore, methods of thought suppression have received considerable attention. However, some studies have found that attempts to suppress thoughts precipitate an increase in thoughts. In the case of substance abuse, such thoughts could serve as cues for further use. This study examined the association between thought suppression and quitting smoking in a sample of current and ex-smokers. Using the White Bear Suppression Inventory (WBSI), scores were obtained for participants' level of thought suppression. Based on the idea that a greater tendency to suppress thoughts would make quitting smoking more difficult, it was hypothesized that unsuccessful quitters would have higher WBSI scores than smokers who had successfully quit. It was found that mean scores on the WBSI were significantly higher (P