Genetic testing of cancer syndromes is based on the existing knowledge of monogenic causes of oncologic diseases. In cases of high-risk genes, the findings concerning the carrier status of pathogenic mutation can be of clinical use in the prediction of risks and for preventive care. In non-carriers in families with mutation in the high-risk gene, the risk of cancer diseases may not be the same as the population risk and some preventive follow-up is recommended. The clinical use of genes with mild or moderate risk of cancer is problematic and could lead to distorted conclusions about the actual cause of the familial form of the disease. Predictive testing in genes with moderate risk of cancer (2-3 times) is not offered, or the non-carriers are followed in the same way as carriers. The use of genes with mild risk is not recommended in clinical practice. Molecular genetic testing also has its limitations and its quality depends on the methods and technology used and the existing knowledge of the significance of mutations. In some variants it is not clear yet whether they are just insignificant polymorphisms or pathogenic mutations. The interpretation of test results in the context of the whole family history is important.