This paper presented findings from research concerned with personality factors and addiction. Four personality measures were examined - level of self-esteem, perceived locus of control, tending to self-deception, and tending to project a flattering self-image. A group of 20 imprisoned heroin addicts was compared with a group of non-addict fellow prisoners and a group of normal controls. Those misusing drugs were found to be significantly lower in self-esteem and less likely to project a flattering self-image than the control group. However, they were similar to the non-drug-using prisoners on all the psychological measures, and this was also found to be the case in terms of socio-economic indices and criminal history.