Epidemiologic studies have identified myriad factors related to cancer risk. Risk can be quantified on the basis of demographic factors, genetics, occupation, medical conditions, and lifestyle. Existing evidence suggests that: (I) individuals at risk often are unaware of their risk; (2) physicians may not know well those factors associated with the highest cancer risk; and (3) methods to reduce risk have been under-applied because of lack of knowledge, lack of funds, or lack of motivation among both patients and physicians. Methods to reduce risk do not follow the usual medical model in that those groups requiring risk-modification intervention usually are symptom free. Evidence indicates that elimination of tobacco use would reduce lung cancer deaths by 83% and substantially reduce the incidence of head and neck malignancies. Broad application of mammographic screening would effect a 30% reduction in breast cancer mortality. Dietary modification could potentially reduce cancer mortality by 30%. An effective program to reduce cancer risk will accomplish the following: (1) develop new and refine existing risk factor measurements to improve identification of individuals at risk; (2) apply risk factor identification and modification more completely to populations known to be at risk; (3) use combinations of risk factors to identify subpopulations at the highest risk; (4) apply existing prevention and screening modalities more broadly and uniformly; (5) identify new screening strategies with improved test performance and cost effectiveness to maximize screening efficiency; and (6) provide accurate and rapid means of risk assessment and quantification using the best available multivariate estimates of risk. An emphasis on education of primary care physicians to practice cancer prevention programs focused on personal risk profiles is reasonable since the populations these physicians serve express risk factors which represent 50% of the attributable risk for cancer in the US. A summary of site-specific risk factors which are amenable to intervention by primary care physicians is provided.