Parent-child communication about tobacco and alcohol use is assumed to be critical to child use of these substances, but it rarely has been systematically described and related to adolescent use. This study included a national sample of 537 adolescent-parent pairs interviewed by telephone at baseline and again 1 year later. Factor analysis of parent reports of communication identified 3 domains: rules and discipline, consequences and circumstances, and media influences. Communication in these domains varied by family characteristics, including parents' substance use and mother's education level. Contrary to assumptions, parent-child communication was not related to initiation of smoking or drinking. Additional analyses suggested, however, that parent-child communication about rules and discipline predicted escalation of use.