This study examined responses to a survey on violence in the workplace from a sample of 8,780 registered nurses practising in 210 hospitals in the Canadian provinces of Alberta and British Columbia. Findings relate to the frequency of violence against nurses, reported as the number of times they experienced a violent incident in the workplace. Nearly half (46%) of those surveyed had experienced 1 or more types of violence in the last 5 shifts worked. Frequency varied by type: emotional abuse 38%, threat of assault 19%, physical assault 18%, verbal sexual harassment 7.6%, sexual assault 0.6%. Further, 70% of those who had experienced violence indicated they had not reported it. Patients constituted the main source of all types of violence. The most prevalent type, emotional abuse, was further explored for its possible determinants. This was also the type of violence most evenly distributed among sources (patients, families, co-workers, physicians). Multiple regression modelling using the individual nurse as the unit of analysis showed the significant predictors of emotional abuse to be age, casual job status, quality of care, degree of hospital restructuring, type of unit, relationships among hospital staff, nurse-to-patient ratios, and violence-prevention measures; using the hospital as the unit of analysis the predictors were found to be quality of care, age, relationships with hospital staff, presence of violence-prevention measures, and province. These findings illustrate important differences in models that use the individual and the institution as the unit of analysis. Implications include targeting prevention strategies not only at the nurse but, perhaps more importantly, at the hospital. Overall, the findings suggest that health-care institutions are not always healthy workplaces and may increasingly be stressful and hazardous ones.