While a growing number of longitudinal studies contribute to our knowledge on the relationship between delinquent peers and one's own delinquent behavior, researchers have generally approached the issue in a restricted way: failing to identify mediating processes or to distinguish between what peers approve of and what they do. Moreover, most studies have used indirect, perceptual measurements, which may have led to biased results. The present study examines the relative effects of peer attitudes toward delinquency and peer delinquent behavior on adolescents' delinquent behavior, using social network data from the School Study of the Netherlands Institute for the Study of Crime and Law Enforcement (NSCR). The results suggest that peer attitudes and attitude transference play a more important role in the social transmission of delinquency than previous research has indicated. Nevertheless, the results also provide evidence for a remaining direct effect of peer delinquent behavior on adolescents' self-reported delinquency. (Contains 13 notes, 3 tables, and 2 figures.)