Background  Medical interventions are often characterized by substantial scientific uncertainty regarding their benefits and harms. Physicians must communicate to their patients as part of the process of shared decision making, yet they may not always communicate scientific uncertainty for several reasons. One suggested by past research is individual differences in physicians’ tolerance of uncertainty. Relatedly, an unexplored explanation is physicians’ beliefs about their patients’ tolerance of uncertainty.Design  To test this possibility, we surveyed a sample of primary care physicians (N = 1500) and examined the association between their attitudes about communicating and managing scientific uncertainty and their perceptions of negative reactions to uncertainty by their patients. Physician perceptions were measured by their propensity towards pessimistic appraisals of risk information and avoidance of decision making when risk information is ambiguous – of uncertain reliability, credibility or adequacy, known as ‘ambiguity aversion’.Results  Confirming past studies, physician demographics (e.g. medical specialty) predicted attitudes toward communicating scientific uncertainty. Additionally, physicians’ beliefs about their patients’ ambiguity aversion significantly predicted these preferences. Physicians who thought that more of their patients would have negative reactions to ambiguous information were more likely to think that they should decide what is best for their patients (β = 0.065, P = 0.013), and to withhold an intervention that had uncertainty associated with it (β = 0.170, P < 0.001).Discussion  When faced with the task of communicating scientific uncertainty about medical tests and treatments, physicians’ perce‐ptions of their patients’ ambiguity aversion may be related to their attitudes towards communicating uncertainty.