We investigated the usefulness of the Over-Claiming Questionnaire (OCQ) as a measure of cognitive abilities. In OCQs respondents are asked to rate their familiarity with items of academic or everyday knowledge (Paulhus, Harms, Bruce, & Lysy, 2003). Some items exist in reality ("reals"), and others do not ("foils"). We developed four OCQs, each consisting of 40 "reals" and 8 "foils" from the domains of Science, Humanities and Civics. The OCQs were administered in a longitudinal rotation design to 112 participants who attended the 9th school grade at the beginning of the study. In latent variable regression analyses 53% of variation in the "reals" could be explained by fluid and crystallized intelligence and over-claiming as indicated by responses to "foils". Further variation in responses to "reals" and "foils" was explained by intellectual engagement. Our results show that self-reported knowledge, although positively related to measures of ability, to a large extent reflects over-claiming. (Contains 2 figures and 4 tables.)