Objective To determine the frequency and types of aggressive and violent behaviors in acute psychiatric inpatient settings and potential interactions between staffing and patient mix and rates of the behaviours were explored. Methods Data on violent incidents were gathered prospectively in two acute psychiatric units in two general hospitals and two units in a psychiatric hospital in Isfahan, Iran. Staff recorded violent and aggressive incidents by using Morrison's hierarchy of aggressive and violent behavior. The classification ranged from level 1, inflicted serious harm to self or others requiring medical care, to level 8, exhibited low-grade hostility. They also completed weekly reports of staffing levels and patient mix. Regression analysis was used to calculate relative rates. Results A total of 400 violent incidents were recorded over a three-month period. Based on the scale, more than 50 percent of the incidents were serious. Seventy-eight percent were directed toward nursing staff. Complex relationships between staffing, patient mix, and violence were found. Relative risk increased with more nursing staff (of either sex), more non nursing staff on planned leave, more patients known to instigate violence, a greater number of disoriented patients, more patients detained compulsorily, and more use of seclusion. The relative risk decreased with more young staff (under 30 years old), more nursing staff with unplanned absenteeism, more admissions, and more patients with substance abuse or physical illness. Conclusions Violent incidents within psychiatric facilities were frequent and serious, with great significance for occupational health. Some clues were found in the prediction of violence. Disclosure of interest The authors have not supplied their declaration of competing interest.