Objective: To better understand the role earlier stressful environments have in predicting functional somatic symptoms (FSS) in late adolescence, this study explores the effect the occurrence of earlier changes in family dynamics and friendship conflict have on FSS. Method: We used data from the Consortium for Longitudinal Studies on Child Abuse and Neglect (N = 1,314), a large, prospective study of children at risk for maltreatment and their parent/caregiver from approximately 4 to 18 years of age. Results: We found a significant, small (Effect Size = .10), positive association between the frequency of family dynamic change during middle childhood (ages 6–12 years) and FSS at age 18 but not during middle adolescence (ages 14 and 16). Conflict with a same-sex best friend at age 16 moderated the association between the frequency of change and FSS. The frequency of family dynamic change in middle childhood and middle adolescence was associated with greater FSS among those who reported greater conflict but not for those who reported experiencing lower conflict. Overall, these effects were specific to friendship conflict and remained when other friendship processes (intimacy and companionship) were included, did not generalize to anxiety/depressive symptoms, and predicted FSS without comorbid anxiety/depressive symptoms. No gender differences were found. The change–conflict interaction differed according to type of family dynamic change (parental vs. residential). Conclusion: Findings emphasize how earlier exposure to frequent changes in family dynamics in middle childhood is particularly associated with late-adolescent health, especially in the context of greater friendship conflict.