Determining whether a hereditary cancer predisposition is present, is important for both the cancer patient and his family. It is relevant for surveillance and prevention or early detection of new tumours, treatment options and issues surrounding the desire to have children. For this reason, it must be ensured that for every patient with cancer (now or in the past) referral for genetic testing is considered. In this article we indicate how to take a family history and where to find and how to apply referral criteria if such a question arises in clinical practice. The consequences of a genetic diagnosis are illustrated by a breast cancer case.