Previous studies have reported significant associations between measures of the family environment and behavior problems in children. However, because children in these studies were genetically related to their parents, such links may not be caused solely by environmental influences. The goal of this study was to investigate genetic influence on associations between family environment and problem behavior using an adoption design. Participants in the study included 179 adopted and 176 nonadopted children, as well as their parents and teachers, in the Colorado Adoption Project (CAP; Plomin, DeFries, & Fulker, 1988). Mothers and fathers each completed the Family Environment Scale (FES) when their child was 1, 3, and 5 years of age; the child's problem behavior at age 7 was rated by both mothers and teachers using the Child Behavior Checklist (CBCL). Patterns of correlations for nonadopted versus adopted boys indicated that associations between aspects of the family's relationship (conflict, cohesion, expressiveness) and behavior problems in home and school were mediated genetically. For girls, however, these links appeared to be influenced by direct shared environmental effects.