Difficulties in communicating diagnostic information are exacerbated when the 'diagnosis' is a 'genetic risk' for cancer. The risk estimation demanded in this situation differs from other types of probability estimations. Observations of participants in 45 consultation sessions between physicians and potential patients were conducted at a clinic for hereditary cancer to explore the communication of genetic information. Thirty-three sessions were audiotaped, transcribed verbatim and analyzed, along with notes from the other sessions. A dominant theme was found to be numerical discussion of risk. Further analysis resulted in the description of problems for practitioners in the process of translating scientific knowledge into clinical management. Problems in providing information include unclear aims of the consultation sessions, mixing various types of background information and probabilities, recognizing how low the predictive values are, and difficulties in communicating the relationship between probability and conclusions. Problems in communicating information about the genetic risk for cancer are of at least two types: dilemmas arising from uncertainties implicit in the nature of the information itself and difficulties in communicating information in a manner that those concerned can interpret. These issues need clarification, so that information with far-reaching consequences can be made as clear and comprehensible as possible for those involved.