Given the widespread appeal of conspiratorial beliefs, it is surprising that very little empirical research has examined the psychological variables associated with such beliefs. In the present study, we examined individual and demographic predictors of beliefs in conspiracy theories concerning the September 11, 2001 (9/11) attacks on the World Trade Centre and Pentagon among a representative British sample of 254 women and men. Results of structural equation modelling showed that 9/11 conspiracist beliefs were positively associated with belief in other conspiracy theories, exposure to 9/11 conspiracist ideas, political cynicism, defiance of authority and the Big Five personality factor of Agreeableness. In total, a model including demographics, personality and individual difference variables explained over 50% of the variance in 9/11 conspiracist ideas. The implications of these findings for the literature on conspiracy theories are discussed.