The testing of individuals before the age of 18 years for hereditary late-onset diseases has been judged ethically not acceptable in guidelines and directives published by medical professional organizations. However, there are not enough best interest arguments to deny genetic testing to an adolescent at risk of carrying a BRCA1 mutation, even if the competence of adolescents for medical decisions is considered to be lower than the competence of adults. The adolescent's decision is not irrational or of very high risk. Respecting adolescents' autonomous choices concerning genetic testing has positive consequences for their self-esteem and psychological health. Geneticists and other professionals should clearly differentiate between children and adolescents in regard to BRCA1 gene testing and recommend giving decision autonomy about the test to all psychologically "normal" adolescents.