Background: The allostasis theory postulates that stress causes the body to activate physiologic systems in order to maintain stability. Objective: The authors sought to examine the relationship between earlier stress and later development of breast cancer (BC). Methods: Authors correlated discrete and interactive relationships of stressful life events, social support, and well-being during childhood and adolescence with the occurrence of BC in adulthood among 300 women with primary BC and 305 matched control subjects. Results: BC patients and control subjects reported similar childhood experiences. Yet, although childhood stressful life events were associated with reports of less family support and well being among the controls, those in the BC group who experienced high stress in early childhood actually expressed higher levels of family support and well-being than did those who had experienced lower levels of stress. Conclusion: These findings may reflect a tendency toward a repressive coping style among the BC group, which may be either a risk factor for the disease or a result of having it.