The stresses and uncertainties of cancer can be overwhelming for families. The Family System Illness model offers a psychosocial map to address these challenges and to make the inevitable strains more manageable. It provides a set of terms and a common language within a framework that attends to the longitudinal, psychosocial pattern of a health condition within a multigenerational, life cycle, and belief system context. Such a psychosocial framework can facilitate collaborative, effective coping and adaptation, thereby enhancing the quality of life for families affected by cancer. The model's utility is discussed for research, preventive screening, family assessment, treatment planning, and service delivery in a wide range of healthcare settings. Cancer 2005. © 2005 American Cancer Society.