After the paper by Mayo, White, and Eysenck in 1978, a considerable number of papers studied the so-called sun-sign-effect predicted by astrology: people born with the sun in a positive sign are supposed to be extraverted, and those with the sun in a negative sign are supposed to be introverted. In these papers, researchers used ad hoc questionnaires with a few questions related to belief, knowledge, experience, or attitude toward astrology. However, an appropriate inventory with known psychometric properties has yet to be developed to assess the belief in astrology. In the present paper, the Belief in Astrology Inventory is presented with some psychometric data. The participants were 743 undergraduates studying Psychology and Social Sciences at a university in Spain. Correlation of scores on Belief in Astrology and Extraversion was small but significant (r=.22; r2=.04) for positive sun-sign participants. This value accounts for negligible common variance. Women had significantly higher scores on the inventory than men. [ABSTRACT FROM AUTHOR]