The paper aims to stimulate reflection and debate on the issue of uncertainty as a key component of nuclear or radiological emergency management. It identifies and discusses different types of uncertainties that appeared during and after real emergencies. For this, seven different case studies of nuclear and radiological events have been analysed using three separate methodological approaches: i) case descriptions (document review); ii) media analysis; and iii) semi-structured interviews. The overall objective was to elucidate the understanding and response to scientific and social uncertainties, and related ethical issues. A range of different uncertainties were identified and roughly grouped into categories related to: 1) technical and measurement uncertainties; 2) societal impacts and societal framing; 3) contradictory information and communication aspects; 4) ethical aspects. This analysis intends to inform emergency managers on the types of uncertainties that may appear to different actors during nuclear or radiological emergency. The results should serve to stimulate preparation on the uncertainty response and by this also to reduce some of the identified uncertainties.