The aim of this prospective study was to evaluate the consequences of the disclosure of a positive genetic test result to patients affected with cancer. Personal repercussions and patients' behavior with the transmission of their results to relatives were considered. We conducted semistructured interviews with 23 cancer patients identified as carriers of a cancer-predisposing mutation for hereditary breast ovarian or nonpolyposis colorectal cancers, 1 month after the disclosure of the test result. Eight patients spontaneously expressed distressed reactions ("you no longer feel cured"), and 14 patients reported at least one negative feeling (dissatisfied, discouraged, unhappy, or worried), despite expecting to be a carrier. Sixteen patients expressed concerns about the risk of developing another cancer, and 18 were concerned for their children's future, in that they may carry the mutation and develop a cancer. Although 8 patients found that disadvantages of knowing their genetic status outweighed the advantages, all but 1 did not regret having undergone genetic testing. All of the patients transmitted their results to at least one close relative. Although 6 of them expressed difficulties in being the only person who could transmit the information and 9 said it was a heavy responsibility, all except 1 did not want someone else to have to inform their families. Our results illustrate the potential negative impact of diagnostic genetic testing in patients with cancer. This includes distressed reactions and difficulties in transmitting their results to relatives. Future large-scale studies are warranted to confirm our findings.