Three patients, a 45-year-old man, a 51-year-old woman and a 43-year-old woman, wanted to know whether they had a hereditary predisposition for cancer. The family of patient A fulfilled the clinical diagnostic criteria for hereditary non-polyposis colorectal carcinoma (HNPCC). The family of patient B fulfilled the clinical diagnostic criteria for hereditary breast/ovarian cancer (HBOC). The family of patient C did not completely fulfil the criteria for HBOC since only two family members had a confirmed diagnosis of breast cancer. In all three families, DNA-mutation analysis was performed. In families A and B no mutation was found. However, based on the family history, the diagnosis of hereditary cancer was made and recommendations for surveillance were given. After extensive counselling, one member of family B eventually decided to have prophylactic surgery performed. A few years later, a pathogenic mutation in BRCA2 was found in family B. In family C, an unclassified variant was found in BRCA1. Further investigations in the family were not possible, due to a lack of co-operation from family members. It is important to obtain a thorough and complete family history. When DNA-analysis remains inconclusive or if an unclassified variant is found, recommendations for surveillance will be based on this family history.