Familial clustering of cancer is well known from epidemiologic studies. This can be due to chance, shared environmental influences, shared genes and chance-environmental-genetic interactions. Family studies are a key to the understanding of the environmental and genetic etiology of chronic disease. Cancer families are human models of susceptibility to neoplasia. More and more people are aware of, and anxious about, their cancer risk. High-risk individuals can benefit from prevention and early detection programs. In medical practice the patient workup should include a carefully obtained family history. This low technology method has the potential for reduction of cancer morbidity and mortality. Every person should create his/her own family tree and discuss it with his/her doctor. This is a step each individual can take for his/her health.