Since the introduction of Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III) in 1980, there has been a growing interest in the study of patients with substance use disorders (SUD). The driving force behind this field has been, and still is, the high clinical pessimism about the prognosis, and the difficulties in the clinical management of the characteristics of diagnosed patients. In this way the important matter to study is the evaluation of co-occurring personality problems and substance abuse. So the study investigated the personality traits of addicted and nonadicted people.

101 addicted people and 101 nonaddicted people were randomly selected and Mc Care & Costa's NEO PI-R inventory was administered on them. Mean scores were compared with T independent tests.

Findings indicated that there are differences among means of personality traits in two groups. Addicted people are more neurotic and open to experience than nonaddicted people and nonaddicted people are more extroverted, agreeable and conscientiousness than addicted people.

Findings showed addicted people are more neurotic and open to experience than nonaddicted people and nonaddicted people are more extroverted, agreeable and conscientiousness than addicted people.It indicates that evaluating with reliable measures and with more attentions to personality traits can help the psychiatrists and psychologists to diagnose the cause of tendency to addiction and also reduce the psychological problems that is related with addiction before and in during drug treatment and can reduce duration of treatment and enhance efficacy of treatment methods.