Epidemiologic studies have demonstrated that virtually every form of human cancer may aggregate in families. Genetic susceptibility plays an important role in the development of many of these cancers, yet until very recently genes associated with this susceptibility had not been identified. Over the last several years, the class of genes known as tumor suppressor genes has been most consistently implicated in hereditary cancers. Recently, genes associated with childhood tumors including retinoblastoma, Wilms' tumor, as well as with adult-onset tumors such as breast cancer and colon cancer have been either cloned or localized to specific chromosomal sites. Their isolation has encouraged the development of techniques with which to analyze cancer-prone individuals and families for the presence of germline, or constitutional, alterations of genes that may place them at high cancer risk. In the past year, the benefits and pitfalls of some of these screening assays have been studied. Also, the literature has indicated the importance of considering both ethical and psychosocial implications of our growing ability to perform predictive testing for cancer.