The present study provides evidence supporting the presence of a General Factor of Personality (GFP), which has been proposed to represent the apex of the hierarchy of personality traits. Furthermore, the construct validity of this general factor is assessed to address recent criticisms suggesting that the GFP may merely be a statistical artefact rather than a genuine higher-order personality dimension. In this study, two samples of monozygotic (MZ) and same-sex dizygotic (DZ) twins completed the NEO Personality Inventory-Revised (NEO-PI-IR), assessing individual differences in the Big Five traits of personality, and the Dimensional Assessment of Personality Problems–Differential Questionnaire (DAPP-DQ) measuring variance in abnormal personality traits. First unrotated factors were extracted from each of the two measures separately within each sample. Correlations between these factors were significant and high in both samples (.78 and .77), indicating that the factors represent similar constructs. The manner in which these findings help to validate the GFP is discussed.