Internalizing symptoms (withdrawn/depressed and anxious/depressed), measured by the Child Behavior Checklist (CBCL), were examined as related to the development of externalizing problems, a pathway to risky behavior. A cross-section of children ages 6 to 15 was drawn from the National Institute of Child Health and Human Development's (NICHD) Study of Early Child Care and Youth Development (SECCYD) longitudinal data set of 1,364 families with full-term, healthy newborns throughout the United States. Internalizing and externalizing scores were determined through mothers' reports on the CBCL. When considered separately and together, internalizing symptoms significantly related to externalizing behaviors, with "anxious/depressed" accounting for the greatest proportion of variance. As age increased, internalizing symptoms accounted for a greater degree of externalizing problem variance. Sex was a significant moderator. Results suggest the utility of identifying and treating internalizing problems early, which may reduce the occurrence of externalizing and risky behaviors such as substance abuse. (Contains 7 tables.)