Purpose. This study aims to advance the original formulation of Eysenck's theory of criminality from the factorial level to suggest that primary scales of personality best determine reports of delinquency. Method. Two self-report studies were conducted. The first consisted of 101 students and the second used an additional 101 students. The first study used measures of Self-Reported Delinquency (SRD) and Socialisation (Gough & Peterson, 1952) and the Eysenck Personality Questionnaire Revised Edition (EPQ-R; H.J. Eysenck & Eysenck, 1991). The second study complemented the first study to utilize the EPQ-R and SRD only. Results. A series of exploratory hierarchical multiple entry regressions of the factors in the first study demonstrate that high Psychoticism predicts SRD, whereas high Psychoticism and Neuroticism predict Under-socialization. The primary scales of Disrespect for Rules, Depressed and Need for Stimulation significantly predict both criteria. The second study extends the first study through structural equation modelling to provide acceptable evidence of the concurrent validity of these primary scales with SRD. Conclusions. We propose that the significant primary scales of personality provide a clear reformulation of Eysenck's original theory of criminality as they explain the variance in delinquency and socialization in a systematic manner. Furthermore, primary scales provide a theoretical framework for behavioural interventions, as required by Blackburn (2000).