Loneliness and antisocial behavior were predicted from religiosity and positive religious coping in this 1-year longitudinal study of 564 16-year-old Indonesian Muslim adolescents. An externalizing behavior construct was formed from 3 variables (i.e., self-reported tobacco and alcohol use, self-reported problem behavior, and peer-rated aggression). Loneliness was self-reported. Externalizing behavior was significantly predicted by religiosity in concurrent analyses and marginally predicted by religiosity in the longitudinal analyses. In contrast, positive religious coping predicted loneliness both concurrently and longitudinally. These results are consistent with the view that Islam religiousness is multifaceted and that specific aspects of Islamic religiousness are differentially associated with youth adjustment.