Understanding of the neoplastic events involved in heritable colorectal cancer syndromes is increasing at the molecular and clinical levels. This knowledge is foundational to cancer chemoprevention, which attempts to inhibit or reverse the tumorigenic process through pharmacologic interventions applied before cancer occurrence. We reviewed all relevant published reports identified from Medline databases (1966-1998) regarding cancer chemoprevention in familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, and heritable colorectal cancer cohorts, including rodent models of these diseases. Additional references were obtained from citations listed in the reviewed reports. A large amount of experience exists with cancer chemopreventive agents in both genetically-based rodent models and patient populations with familial adenomatous polyposis. These studies have provided important data on the natural history of neoplasia in this syndrome and have identified several classes of compounds with chemopreventive activity. Cyclooxygenase inhibitors, for example, yield substantial cancer prevention in animals and adenoma regression in humans, although reductions or delays in cancer incidence have not been proven to date. The data from chemoprevention studies in hereditary nonpolyposis colorectal cancer or other familial nonpolyposis colorectal cancer syndromes are less mature. Persons in heritable colorectal cancer cohorts are at substantial risk for early-onset malignancy in multiple target organs and therefore represent ideal subjects for cancer chemoprevention trials. The goals of chemoprevention are to reduce cancer risk and improve quality of life. Eventual success in family cancer cohorts may be measured through declines in the frequency of invasive surveillance procedures, surgical resections, neoplasia incidence, and cancer-related deaths. Disease-modifying agents that have shown promise in preliminary efficacy trials with intermediate endpoints require further testing to establish definitive clinical effectiveness. The lessons learned in these high-risk cohorts may have application to the prevention of colorectal cancers arising in the sporadic setting as well.