This study, conducted every 4 years since 1984, is aimed at monitoring alcohol, tobacco, tranquillizers and illegal drug-use trends among 15-year-olds from Warsaw. The self-report data are taken from a representative sample of students attending schools in three districts of Warsaw (sample size ranged from 1461 to 3918 in the different study waves). Between late 1980s and mid-1990s a significant increase in youth substance use, including alcohol, cigarettes and illegal drugs, has been documented. The most recent results (from 2000 to 2004) indicated stabilization in alcohol and illegal drug use and decrease in tobacco use. The trend in the use of tranquillizers/sleeping pills was relatively stable over the past 16 years. However, changes in adolescent substance use differ across gender. While boys as a group became more restrained in substance use, girls remained at the same level or continued to show increasing trends (e.g. in getting drunk). These differences reflect changes in young female risky behaviours. (Contains 8 tables, 1 figure and 1 note.)