Relational Frame Theory proposes that levels of sophistication with relational concepts may underlie intellectual performance. In order to further elucidate this relationship, the current study examined correlations between scores on a novel Relational Abilities Index (RAI) and a range of widely-used cognitive ability measures, including Full Scale IQ. In Study 1, 35 adult participants completed a battery of cognitive assessments, comprising of the National Adult Reading Test, the Rey Auditory Verbal Learning Test, the Trail Making Test, the Cognitive Failures Questionnaire and a RAI assessment at two time periods. In Study 2, a full WAIS-III assessment and RAI was administered to 25 college students. Results indicate that performance on the RAI displayed impressive degrees of correlation with the three main IQ indices, three of the four IQ subindices, and three of the four cognitive ability measures, suggesting that the RAI assessment may represent a promising potential proxy measure of Full Scale IQ.