To ascertain current levels of drug use among teenagers and to examine interrelationships in use, a two-stage cluster sample of Victorian secondary school students in years 7 (aged 12 to 13 years), 9 (14 to 15 years) and 11 (16 to 17 years) were surveyed using a questionnaire on computer. Tobacco use and alcohol consumption were evaluated by self-reported frequency of use and seven-day retrospective diaries. Marijuana and coffee consumption were assessed by self-reported frequency of recent use. The questionnaire was completed by 2525, a participation rate of 83 per cent. Tobacco use rose with year, with 24 per cent of young women and 16 per cent of young men in year 11 being regular smokers. Trends across year level for heavier alcohol consumption were also observed, with just under 10 per cent of year 11 students reporting a weekly consumption higher than the current recommended guidelines for adults. Strong interrelationships in drug use were found, with a pattern of association between smoking and drinking consistent with a mutual elevation of risk. Frequent use of tobacco and alcohol had a high risk for associated marijuana use. Coffee consumption carried a significant independent association with regular smoking. Teenage substance use is common and most occurs at low level and frequency. However, for a substantial and increasing minority across the teenage years, high levels of tobacco and alcohol consumption potentially compromise health. Frequent alcohol or tobacco use rather than heavy intermittent consumption is most likely to be associated with concurrent substance use potentially damaging to health.