The explosion in molecular technology has brought with it a new era in medical genetics. In the past, genes easiest to work with were those responsible for heritable disorders manifesting in childhood that were often the consequence of metabolic derangements. The disorders were detectable either at birth or soon after either because of physical appearance or the development of a clinical problem. It is now possible to identify genes that confer increased susceptibility to diseases that may not be manifest until late adulthood, such as cancer or heart disease. This review discusses conditions in which children may now be identified as genetically at increased risk for cancer development in childhood or adulthood, and current dilemmas regarding appropriate screening strategies for these at-risk individuals.