Even though it clearly exists, antisocial behavior that begins in mid- to late adolescence does not fit into commonly accepted taxonomies of antisocial behavior. Utilizing participants from the Minnesota Twin Family Study (MTFS), an epidemiological study of twins and their families, this study examined how this course of antisocial behavior compared with persisting (beginning before age 15 and continuing after age 15) and desisting (stopping before age 15) antisocial behavior in terms of risk for later substance dependence and background risk factors. The results of the study support the notion that antisocial behavior that begins in mid- to late adolescence is pathological and associated with increased rates of substance dependence several years later. Study limitations and implications are presented and discussed. Tables, references