OBJECTIVE-Understanding how young girls respond to growing up with breast cancer family histories is critical given expansion of genetic testing and breast cancer messaging. We examined the impact of breast cancer family history on psychosocial adjustment and health behaviors among >800 girls in the multicenter LEGACY Girls Study.METHODS-Girls aged 6 to 13 years with a family history of breast cancer or familial BRCA1/2 mutation (BCFH+), peers without a family history (BCFH−), and their biological mothers completed assessments of psychosocial adjustment (maternal report for 6-to 13-year-olds, selfreport for 10-to 13-year-olds), breast cancer-specific distress, perceived risk of breast cancer, and health behaviors (10-to 13-year-olds).RESULTS-BCFH+ girls had better general psychosocial adjustment than BCFH− peers by maternal report. Psychosocial adjustment and health behaviors did not differ significantly by selfreport among 10-to 13-year-old girls. BCFH+ girls reported higher breast cancer-specific distress (P = .001) and were more likely to report themselves at increased breast cancer risk than BCFH− peers (38.4% vs 13.7%, P < .001), although many girls were unsure of their risk. In multivariable analyses, higher daughter anxiety was associated with higher maternal anxiety and poorer family communication. Higher daughter breast cancer-specific distress was associated with higher maternal breast cancer-specific distress.CONCLUSIONS-Although growing up in a family at risk for breast cancer does not negatively affect general psychosocial adjustment among preadolescent girls, those from breast cancer risk families experience greater breast cancer-specific distress. Interventions to address daughter and mother breast cancer concerns and responses to genetic or familial risk might improve psychosocial outcomes of teen daughters.Although studies have reported psychosocial adjustment in children of parents with cancer, few studies have evaluated outcomes in youth from families at familial or genetic risk for breast cancer. Understanding the impact of growing up in a family at risk for breast cancer is The LEGACY Girls Study is the first to focus on preadolescent girls growing up in families with breast cancer risk, including girls whose mothers have not had breast cancer. 39 This study addresses limitations of previous studies by being theoretically informed and including sociodemographically diverse girls, an unrelated comparison group, and both parent and child report. We applied a novel conceptual model 40 grounded in the Self-Regulation Theory of Health Behavior 41 and developmental theory. 34,37 Our model posits that response to a health threat, including psychosocial adjustment and the performance of health and risk behaviors, is a product of one's perceptions of the threat. [40][41][42] This model is ideal for the study of youths' maturation because it emphasizes "commonsense" representations, encompasses sociocultural factors, and is iterative and dynamic, providing a unique opportunity to examine chang...