Studying epistemically unwarranted beliefs (EUB) is relevant at basic, applied, and social levels. However, EUB scales validated in Spain are scare. Consequently, we aimed to develop and validate a scale of this kind. One thousand four hundred and sixty participants answered to a preliminary version of the questionnaire. Exploratory and confirmatory factor analyses revealed the final form of PEUBI: a 36-item instrument with five related factors (Superstitions, Occultism and Pseudoscience, Traditional Religion, Extraordinary Life Forms, and Conspiracy Theories). The results showed that the items were little affected by social desirability bias. PEUBI factor scores showed good internal consistency (estimates between 0.85 and 0.97), test-retest reliability (estimates between 0.75 and 0.93), and convergent-divergent validity. Sociodemographic differences were also explored, observing lower levels of EUB in men, elders, from pure sciences and technology, and atheists. In conclusion, PEUBI is a valid and reliable psychometric instrument to assess paranormal, pseudoscientific and conspiracy beliefs in Spanish adults.