The predictions of Cloninger's neurobiologic learning model on the relationships between novelty seeking (NS), harm avoidance (HA), reward dependence (RD), and persistence (P) and the traditional DSM-III-R personality disorders (PDs) were tested on a sample of 2, 889 (1, 475 males and 1, 414 females) Italian high school students aged 16 to 18 years, using the Structured Clinical Interview for DSM-III-R Personality Disorders-self-report (SCID-II) and the Tridimensional Personality Questionnaire (TPQ). All relationships were in the predicted direction for antisocial, narcissistic, avoidant, and obsessive-compulsive PD alone, and at least two were in the predicted direction for schizoid, histrionic, borderline-explosive, dependent, and passive-aggressive PD. Eight of nine relationships were in the predicted direction for NS, but only seven of nine for HA and RD. This study provides substantial support for Cloninger's neurobiologic learning model as a useful tool to describe and classify personality variants and, because of the supposed neurochemical implications, to link personality traits to the underlying neurochemical and neuroanatomic substrate. (C) 2000 by W.B. Saunders Company.