Parents strongly influence children's health, yet how parents continue to shape the health of midlife adult children remains unknown. Moreover, while most adults are married by midlife, research has failed to identify the effects of parent-in-law relationships on midlife adult wellbeing. Using interviews with 90 individuals in 45 marriages, we investigate how midlife adults perceive the influence of parents and parents-in-law on adult child health. Findings reveal that particularly mothers and mothers-in-law positively influence child's health via support during, or in anticipation of, illness and injury. The health experiences of parents and in-laws, particularly fathers/in-law, become cautionary tales preparing adult children for future health issues. Yet, parents/in-law also have negative influence on adult children during midlife due to parents' compounding health needs. We use family systems theory to show how parents/in-laws are intertwined in ways that influence health during children's midlife that has ramifications into later life.