The present study examined the independent and interactive relations of effortful control and two family environment variables (parent-adolescent conflict and negative family relations) on the subsequent conduct problems and depressive symptoms of 459 European American and Latino adolescents between the ages of 10 and 14. Hierarchical regression analyses showed that even after baseline levels of conduct problems were taken into account, lower levels of effortful control and poorer family relations were uniquely predictive of more conduct problems 1 year later. A three-way interaction among effortful control, negative family relations, and ethnicity indicated that among European Americans only, effortful control moderated the negative family relations effect. High levels of effortful control protected European American adolescents living in homes characterized by negative family relations from elevated levels of subsequent conduct problems. Contrary to findings for the conduct problems outcome, only baseline levels of depressive symptoms predicted subsequent depressive symptoms. (Contains 3 tables and 1 figure.)