Patients over the age of 75 are responsible for more than half of physical assaults on NHS staff in hospitals across England, figures show.
NHS Protect, which gathered the data, says the stress and confusion of a hospital stay may explain the findings.
They looked at thousands of incidents, ranging from bites and pinches to the most serious attacks on medical staff.
Over-75s accounted for 57% of violent incidents on wards between 2010 and 2015.
Yet, according to figures from the Health and Social Care information Centre, in the same five-year period, people over 75 made up about 24% of patients being treated by hospital consultants at any one time. This suggests a disproportionate number of incidents on wards involved older people.
About 4% of the assaults involved male and female patients who were over 100 years old.
NHS Protect, which leads on work to identify and tackle crime across the health service, says theirs is the most detailed ever review of violence directed at NHS workers.
They say the high proportion of reported physical assaults by elderly patients probably reflects the challenges of dealing with older people coping with the confusion of a hospital stay, compounded by conditions such as dementia.
More than half of the 6,762 assaults between 2010 and 2015 resulted in injuries, yet only about 7% of the acute sector staff reported the incidents to police.
NHS Protect is now calling for staff to come forward and report every incident so that procedures can be changed to keep staff and patients as safe as possible.
David Dixon, from NHS Protect, told BBC Radio 5 live: "The next step is for individual trusts to study our findings and identify what lessons they can learn for their own particular contexts, about where best to place their resources.
"And we continue to ask staff never to accept assault as 'just part of the job'. Every physical assault should be reported, in the established way."
NHS Protect has developed guidance and other resources to help NHS staff prevent and manage challenging behaviour by focusing on minimising a patient's distress.
David Hope, an NHS nurse for the past 14 years said: "If you include all the scratches, nips and pinches, I've been assaulted 20 or 30 times.
"We're supposed to report every incident, but you'd spend all your time on a computer if that happened."
Mr Hope said the reaction of relatives who had witnessed an assault was also upsetting.
"The assumption from relatives is that we are doing something wrong - that's why the patients attacked us," he said.
"We've often been trying our best, and it isn't recognised."