The Multidimensional Perfectionism Cognitions Inventory (MPCI; Kobori Tanno, 2004) is a promising new instrument developed in Japan to assess perfectionism cognitions regarding personal standards, pursuit of perfection, and concern over mistakes. In this study, we examined reliability and validity of the English version of the MPCI, the MPCI-E (Kobori, 2006), in a sample of 371 native English speakers. A confirmatory factor analysis confirmed the MPCI-E's 3-factorial oblique structure. Moreover, correlations with measures of dispositional perfectionism and past-week positive and negative affect provided initial evidence of the MPCI-E's convergent and differential validity. Finally, hierarchical multiple regressions indicated that the MPCI-E showed incremental validity in explaining variance in positive and negative affect above variance explained by dispositional perfectionism. Overall, the findings provide initial evidence for the reliability and validity of the MPCI-E as a multidimensional measure of perfectionism cognitions that has the potential to further the understanding of positive and negative cognitions in perfectionism.