Aims: The current research assessed the rate of substance use among Iranian secondary school students. Participants: 470 boy secondary school students selected randomly and were assessed. Measurements: A confidential questionnaire based on DSM-IV and a prior study was distributed, completed by the students and collected in the same sessions in 2001. Results: Their mean age was 13.6 yr (SD = 0.67) ranging from 12 to 14. Of the subjects 105 (22.3%) reported usage of substance (s) once or more sometime during their lives: tobacco 82 (17.5%) alcohol 32 (6.8%), opium 3 (-0.6%), hashish 1 (-0.2%), and heroin 2 (0.4%). Only 39 (8.3%) of the students were current substance dependent: 29 (6.2%) were tobacco dependent and 13 (2.8%) were alcohol dependent. Some were using more than one substance. Conclusions: Tobacco and alcohol were found to be the most prevalent form of substance use. Seeking pleasure, modeling and release of tension were the most common reasons for initial substance use. The most common reasons reported for current use were seeking pleasure, habit and release of tension, respectively. These findings can be implicated in planning preventive programs. Some of the findings are different from those carried in the west. Cultural attitudes could be the causes of the differences.