The White Bear Suppression Inventory [WBSI; Wegner, D. M. & Zanakos, S. (1994), Journal of Personality, 62,615-640] is a self-report questionnaire measuring people's general tendency to suppress unwanted negative thoughts. The current article describes two studies investigating the reliability, factor structure, validity, and correlates of the WBSI. Study 1 (n = 172) showed that the WBSI is a reliable instrument in terms of internal consistency and test-retest stability. Factor analyses of the WBSI revealed a I-factor solution. Furthermore, the WBSI was found to correlate positively with measures of emotional vulnerability and psychopathological symptoms. In Study 2 (n = 40), the relationship between WBSI and levels of intrusive thinking was examined in more detail, using a thought suppression task. In general, results of this thought suppression experiment provided evidence for the validity of the WBSI. That is, subjects with high WBSI scores exhibited higher frequencies of unwanted intrusive thoughts than subjects with low WBSI scores.