Introduction: Addiction is one of the most important psychosocial injuries in our country. Estimation of number of addicts in communities have always been a difficult and and controversies. The aim of the present was to estimation of number of addicts to drug abuse addicts by using capture-recapture method in Ilam city.
 Materials & methods: Data were collected by using questionnaire based on check list and capture-recapture method from addicts referring to addiction treatment centers and camps. Then, geometric probability distribution was used to estimate the number of hidden population of drug users with 95% confidence interval.
Findings: There were 1713 addicts in recovery campuses in Ilam city. According to capture recapture methods, it is estimated that the number of addicts in this city is within 7939 people (95% CI: 6694-9184). So, percent of drug users than total population 15 years and over of the city was estimated 10%. Also, the use of drugs among identified addicts illustrated that use of drugs was started with 28% in the 70s and in 80s have increased to extremely alarming rate of 67.2%.
 Discussion & Conclusion: The overall results of the study indicate that addiction has an increasing trend in Ilam and its growth in was began in 1370s and accelerated in late 1380s and a shift is happening from use of traditional materials (such as drugs) to the new drugs, industrial and kitchen (such as glass and crack).