Cancer cases are often clustered in certain families and pedigree analysis indicates that at least 5% of cancer patients have a genetic predisposition to the disease. During the past decade the basic mechanisms for hereditary cancer have been outlined and a large number of the genes involved have been identified. This rapid development has changed the clinical management of cancer families, which now includes surveillance programs directed to early diagnosis of tumors as well as predictive mutation testing to identify gene carriers. This review outlines the molecular basis for hereditary cancer that has become the basis for genetic counseling of cancer families. The organization of clinics for cancer families in Sweden and the clinical implications of surveillance programs and gene testing for cancer predisposition are discussed.