In this study, we present the Pseudoscientific Belief Scale (PSEUDO; [alpha] = 0.90). The conceptual foundations of the scale include (a) a philosophically grounded and functional demarcation criterion between science and pseudoscience; (b) an analysis of the pseudoscientific status of science denialism, which is integrated into the scale; and (c) a bibliographic justification to back up the inclusion of each item. The validation process is carried out based on two studies. Study 1 (N = 3,416) uses both exploratory factor analysis and cluster analysis: Conceptually congruent factors are not reported. Study 2 (N = 292) includes a total of 21 sociodemographic, personality, and cognitive independent variables, as well as the two thematic subscales of PSEUDO as dependent variables, in order to analyze the psychological profile of both sets of believers. Results show high similarity between both groups, confirming construct validity.