A substantial proportion of adolescent antisocial behaviour (ASB) research has focused on identifying the chronic offender; comparatively little research has investigated developmental patterns among the general adolescent population, who account for a large proportion of ASB participation. A modified version of the Mak Self-Report Behaviour Scale was administered to 233 (relatively advantaged) community adolescents (aged 9–17), and 193 young adults (aged 18–25). Not available in previous instruments, in addition to prevalence rates, the Adolescent ASB Scale (AASBS) accurately identifies specifically when adolescents enter, exit, and peak in their ASB participation. An earlier age of ASB participation was associated with greater frequency, severity and duration. The most noteworthy finding was a mid-adolescent peak in ASB participation, which was shorter and more dramatic for girls. These findings provide knowledge critical for informing future research into causal explanations for the temporary and dramatic increase in adolescent ASB, and for developing more effective intervention practices with mainstream youth.