How long counselees retain the information given during their genetic consultation is of major importance. To address this issue, we conducted a survey among the 3500 families that have been offered genetic counseling at our Center since 1988. In August 2007, we mailed a questionnaire to a representative subset of 579 persons belonging to breast/ovarian or colon cancer families seen in the last 10 years, either carrying an identified mutation or not. Targeted topics included the meaning of hereditary predisposition, the medical prevention related to the familial risk, the steps to undertake for a new family member to enter the genetic testing program and general knowledge of hereditary predisposition to cancer. A total of 91 randomized non-respondents were sent a second, more inciting letter, in order to assess any non-response bias. Overall, 337 questionnaires were collected: response rate was 58%. Standardized average knowledge was 7.28±1.52 of 10. Scores were lowest concerning medical prevention. The level of knowledge decreased with age (P<10(-6)), but increased with educational level (P<10(-5)) and mutation status (P=0.01). Surprisingly, no erosion of patients' knowledge over the time was observed (P=0.41). Among persons at hereditary risk of colon cancer, the level of knowledge tended to improve with time, in contrast to the breast/ovarian group (P=0.017). Among persons with a familial risk of breast/ovarian or colon cancer, a renewal of oncogenetic counseling does not seem necessary to maintain the level of specific knowledge. Measures to help patients follow their medical prevention, as organizing or checking their medical examinations, seem indicated.