Background Little is known of the extent to which nursing-care tasks are left undone as an international phenomenon. Aim The aim of this study is to describe the prevalence and patterns of nursing care left undone across European hospitals and explore its associations with nurse-related organisational factors. Methods Data were collected from 33 659 nurses in 488 hospitals across 12 European countries for a large multicountry cross-sectional study. Results Across European hospitals, the most frequent nursing care activities left undone included 'Comfort/talk with patients' (53%), 'Developing or updating nursing care plans/care pathways' (42%) and 'Educating patients and families' (41%). In hospitals with more favourable work environments (B=?2.19; p<0.0001), lower patient to nurse ratios (B=0.09; p<0.0001), and lower proportions of nurses carrying out nonnursing tasks frequently (B=2.18; p<0.0001), fewer nurses reported leaving nursing care undone. Conclusions Nursing care left undone was prevalent across all European countries and was associated with nurse-related organisational factors. We discovered similar patterns of nursing care left undone across a cross-section of European hospitals, suggesting that nurses develop informal task hierarchies to facilitate important patient-care decisions. Further research on the impact of nursing care left undone for patient outcomes and nurse well-being is required.