Sociological theories suggest that association with deviant friends is a necessary step on the path to early onset of delinquent behavior, while personality theories imply that deviant behavior will be stable from childhood to adulthood. These two rival hypotheses were tested with boys (N = 758) recruited from 53 schools in low socioeconomic areas of Montreal. Disruptive behavior in kindergarten was assessed by teachers; aggression and likability at ages 10, 11, and 12 years were rated by classroom peers; delinquent behaviors at ages 11, 12, and 13 years were reported by subjects. Best friend dyads were created by having boys independently identify each other as one of four best friends. Three independent samples were created to replicate findings at different ages (10–11 years, 11–12 years, and 12–13 years). Results of LISREL analyses from the three samples indicated that the main path toward early onset of both overt and covert delinquency was from kindergarten disruptive behavior to aggression between ages 10 to 12 years, and to delinquency from ages 11 to 13 years. Best friends' behavioral characteristics were associated with the subjects' own behavioral characteristics between ages of 10 and 12 years, but did not explain the level of self-reported delinquency the following year, when the subjects' own behavioral characteristics had been taken into account. Because friends tend to share the same behavioral characteristics, they are more likely to foster continuity in behavior than change. We suggest that the influence of significant peers other than best friends be investigated and that a categorical approach be used to try to identify subgroups of boys who may be highly responsive to peers' influence.