There is evidence that the public perceive blood transfusion as risky, and there is a growing literature exploring factors associated with perceived transfusion risk. One contributory factor might be the types of information different key stakeholders (e.g. general practitioners, anaesthetists, health/life style journalists and blood donors) rely on for information. This article addresses four unanswered questions about transfusion/donation risk, namely (1) do different stakeholder groups perceive different sources of information as more or less trustworthy, (2) to what extent is the perceived trustworthiness related to levels of knowledge and perceived risk, (3) is optimistic bias observed across the stakeholder groups, and (4) is knowledge related to levels of perceived risk across the stakeholder groups? A questionnaire survey was used to assess the trustworthiness of sources of information, perceived risk and knowledge. Four stakeholder groups were examined, namely (1) blood donors (n = 250), (2) general practitioners (n = 88), (3) anaesthetists (n = 143) and (4) medical journalists (n = 20). The results showed that (1) judgements of trustworthiness vary as a function of stakeholder groups, and (2) it is what people think they know rather than what they actually know that is related to judgements of trustworthiness and perceptions of risk. Judgements of trustworthiness are generally unrelated to perceptions of risk, and all stakeholder groups show optimistic bias. The implications of these findings for risk communication, specifically relating to transfusion medicine, are discussed.