One of the most significant risk factors to develop breast cancer is a family history of the disease. Based on family size, structure and age at onset, a distinction is made between "familial" and "hereditary" breast cancer, associated respectively with "low to moderate" and "high" breast cancer risk. About 10 years ago, two major breast cancer genes have been identified: BRCA1 and BRCA2. In about 75% of Belgian hereditary breast and ovarian cancer families a BRCA mutation was detected and several founder mutations were identified. This finding may lead to the development of a cost-effective, rapid, limited molecular test. When a disease-causing mutation is identified in a family member, testing for that specific mutation can be offered to the other at risk individuals. Genetic testing is a multi-step process; it does not only involve mutation analysis but also brings with it the responsability of provoking possible emotional distress as well as discussing appropriate clinical recommendations with persons carrying the mutation. When counselling, special attention has to be paid to several pitfalls: the presence of phenocopies, segregation of more than one mutation in a single family and incomplete penetrance. Families with a strong predisposition for breast/ovarian cancer with a negative test result may have mutations in another (not yet identified) gene or an alteration that cannot be detected with the techniques applied.