en Applicable Applicable <p> <strong> Abstract </strong><strong></strong></p><p> <strong> Background: </strong>Economy, lack of welfare and social services, AIDS and civil war, and also substance abuse are predominant factors that attributes with street children. </p><p> <strong> Method: </strong>576 street children of 10-19 years were evaluated. Data were gathered by demographic and substance use check list. Theses check lists were designed by the researchers and included some simple question about type and duration of substance use. Several psychiatrists confirmed the content of check list. </p><p> <strong> Results: </strong>36.7% of the children had lifetime smoking of cigarette. The frequency of </p><p>  smoking in boys was significantly higher than girls (P<0.05). The mean age of the girls with smoking habit was significantly lower than the boys (P<0.05). </p><p> <strong> Conclusion: </strong>It should be noted that street children are at high risk group for using tobacco. Theses children are also exposed to the dangerous behaviors and sexually transmitted </p><p>  diseases. </p><p>  </p> street children, substance use and Iran 83 87 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-106&slc_lang=en&sid=1 Hamid Reza Ahmadkhaniha 20031947532846001962 20031947532846001962 No Mental Health Research Center of Tehran Psychiatric Institute, Iran University of Medical Sciences,Tehran, Iran. Mitra Hakim shooshtari mitra_hakim2000@yahoo.com 20031947532846001963 20031947532846001963 Yes Iran University of Medical Sciences, Shahid Mansouri Alley, Niayesh Alley, Satarkhan Avenue, Tehran Psychiatric Institute Mehrdad Mohammadian 20031947532846001964 20031947532846001964 No Iran University of Medical Sciences, Mental Health Research Center of Tehran Morteza Naserbakht 20031947532846001965 20031947532846001965 No Mental Health Research Center of Tehran Psychiatric Institute. Farzad Ghazaiepour 20031947532846001966 20031947532846001966 No Mental Health Research Center of Tehran Psychiatric Institute.