The role played by witnesses of bullying in nursing settings remains little studied, despite their potential relevance in explaining the onset and development of bullying. The objective of this study was to develop a model to account for witnesses' intention to help and helping behaviour in response to bullying in a nursing setting. Three hundred and thirty-seven witnesses completed self-report measures of variables predicting intention to help and helping behaviour. A full structural model was constructed using structural equation modelling. The intention to help victims was elicited by tension, group identity, support to peers' initiative to intervene and absence of fear of retaliation. However, engagement in helping behaviour was only predicted by the absence of fear of retaliation. This study shows that witnesses of bullying in nursing settings do not remain impassive, but their experienced discomfort and intention to help victims is not sufficient to predict helping behaviour. Fear of possible retaliation if intervening in favour of victims constitutes a crucial factor explaining witnesses' hesitation to help victims. Several implications for the implementation of policies directed at eradicating bullying in nursing settings are discussed.