This paper presents the results of a study on the Polish version of the Generic Conspiracist Beliefs Scale (GCBS), which was designed to measure individual differences in conspiracist thinking (Brotherton, French, & Pickering; 2013). The Polish version of the scale had excellent internal consistency as measured by Cronbach alpha: .93. The Polish version also had excellent test-retest stability. To check the validity of the questionnaire, various tools were used to measure the characteristics that can be correlated with conspiracist thinking. As a result, it was found that conspiracist thinking is positively correlated with the external locus of control, the results obtained in the Scale of Belief in Zero-Sum Game and the results of the MMPI-2 Paranoia scale. It was also found that patients with paranoid personality disorder and paranoid schizophrenia had higher results on the adapted scale than healthy subjects. In sum, the Polish version of GCBS had satisfactory psychometric properties, which makes it useful for measuring conspiracist thinking.