Compared 934 prisoners with 221 drug addicts' scores on the Eysenck Personality Inventory and examined in detail, using item analysis, the components of the personality factors that differentiated the 2 groups. Prisoners scored significantly higher than addicts on the Extraversion and Lie scales, and addicts scored higher on the Psychoticism and Neuroticism factors. Despite the high levels of criminal involvement among the addicts, they differed from the prisoners on each of the 4 personality factors. There were more differences between the male addicts and prisoners than between their female counterparts. The present findings raise certain questions about the differential management of addicts within prisons. In view of the marked neurotic difficulties and social inhibitions described by addicts, any institution designed to offer help rather than simple incarceration should consider whether the different personality characteristics of addicts require different management regimes. It is suggested that the unusually high Psychoticism scores of many addicts may interfere with conventional therapeutic systems. (13 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)