Primary care physicians are in a unique position to apply recent advances in cancer genetics to the improved care of their patients. Although the impact of our burgeoning knowledge in this area is significant and growing, it is often incompletely understood by the general practitioner. In this article we review the genetic basis of cancer and focus attention on inherited forms of cancer using breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2) as examples. Specific attributes of family and personal history are the most significant indicators of an increased risk of cancer in the individual patient. Genetic testing can be used to further assess risk and guide strategies for cancer screening, prevention, and treatment. However, the decision of whether to pursue genetic testing and the interpretation of results are complex. We review factors involved in these decisions as well as the implications, risks, and benefits of genetic testing for the individual and the family.