An adolescent version of the South Oaks Gambling Screen was administered to 965 high school students, aged 14 to 19 years, in the city of Windsor, Ontario. Ninety percent of the adolescents were involved in gambling activities and a substantial proportion of these were engaged in underage gambling. High levels of problem gambling behaviors were found. Problem gambling behaviors were found to be related to the number of different gambling activities and the amount of money gambled. Problem gambling was defined as a score of five or more on the SOGS-RA screen utilizing a scoring method that paralleled the SOGS scoring method. Problem gambling levels were estimated to be 8.1%±1.8% of the adolescent sample. There were significant gender differences in the level of problem gambling, but no significant difference with age was found.