BACKGROUND: diagnostic uncertainty is ubiquitous. Its communication to patients requires further investigation. AIMS: To determine: 1) What is known about how and why diagnostic uncertainty is communicated in acute care; 2) evidence of the effects of (not) communicating diagnostic uncertainty in the acute setting; 3) associated ethical issues. METHODS: systematic review of Medline, Web of Science and SCOPUS for (acute or emergency care) AND (diagnostic uncertainty) AND (ethics OR behaviours). Critical interpretive synthesis and ethical analysis were conducted. RESULTS AND CONCLUSION: Nine studies (primarily surveys and interviews) were identified. Doctors are not trained in communicating diagnostic uncertainty and perceive it to have negative effects on patients; however not communicating diagnostic uncertainty can disempower patients, resulting in delayed/missed diagnoses or inappropriate use of resource.