This report compares trends in the prevalence of the use of alcohol, cigarettes, cannabis, LSD and cocaine between American and Ontario adolescent students. Data from two repeated cross-sectional epidemiological surveys, one in the USA and the other in the province of Ontario, spanning the years 1975-1997were used. Overall, trends in alcohol, cigarette and cannabis use were similar in both studies: alcohol use has been steadily decreasing since the late 1970s, while both cigarette use and cannabis reached a peak in the late 1970s, decreased throughout the 1980s, and then began dramatic increases in 1992. In contrast, cocaine use has been consistently higher in the USA, especially during the 1980s, but LSD use has been noticeably higher in all time periods among Ontario students. The use of the more common drugs among students in both the USA and Ontario often follow consistent patterns, which suggests that changes in use are due to fundamental shifts in attitudes, rather than the policies or cultural values of a particular country. Less prevalent drugs (cocaine, LSD) show fewer similarities which may reflect deeper cultural differences.