The article reports results from a multiple-cohort, longitudinal study involving 2,430 Norwegian students 10-16 years old. Individual differences in antisocial behavior could generally be measured more reliably in boys than in girls, at an earlier age and with a greater number of scales. Students who took part in more serious antisocial acts were to a much greater extent involved in less serious offenses as well. There were substantial correlations between smoking and use of alcohol and the core antisocial scales, suggesting that such behavior may represent a kind of norm-breaking, antisocial behavior in these age-groups. A set of analyses involving expected sex and age differences, differences between self-reported arrested and non-arrested subjects and correlations with a number of conceptually related variables attested to the construct validity of the key scales included in the questionnaire. The new questionnaire should be useful for studying the development, causes, and correlates of antisocial behavior in relatively young populations. Tables, figure, references, appendixes