Familial adenomatous polyposis (FAP) is a well-defined, inherited colorectal cancer syndrome due to mutations in the APC gene. Genetic counseling and predictive gene tests for FAP will likely be incorporated as a first step in risk assessment for this condition. Our experience with predictive gene testing for FAP sheds important light on the impact of such tests for families at risk for FAP or colorectal cancer. We counseled and tested 47 adults and 36 minors at risk for FAP. Gene test results changed the risk of FAP for a given individual from a priori 50% to essentially zero or 100%. These individuals and their family members were interviewed before and after disclosures of APC gene test results to examine issues related to patients' knowledge about FAP, risk perception, reasons for seeking gene testing, and anticipated meaning of the results. We found that the gene test is imbued with meaning beyond determination of gene status in families who choose gene testing. The at-risk patient has preformed, well-entrenched conceptions of what having FAP or colorectal cancer entails, and family relationships and identity may be strongly linked with disease or gene status. We have found that genetic testing of minors requires additional counseling considerations and effort to ensure their understanding of FAP and the gene test. Importantly, their understanding of the clinical and social meaning of the gene test result must be elicited. For all patients, the value of counseling includes reduction of uncertainty and adjustment of misperceptions. Genetic counseling guidelines for this emerging clinical service are presented.