[Uncertainty regarding patient information: insecurity or chance?].

There is a considerable amount of uncertainty regarding the care of individual patients. The present paper describes the handling of uncertainties in patient care and its relevance for shared and informed decision-making. What affects the physician-patient relationship, and which strategies may contribute to communicating uncertainties in a constructive manner? Data from clinical trials describe and reduce our knowledge about uncertainty of treatment effects. Regarding rare diseases, however, we are faced with methodological limitations since randomised controlled trials (the highest level of evidence) are not feasible. But other 'low-level' evidence is available and should not be neglected but systematically collected and evaluated as resources for further research activities.