Thousands of workers took sick leave to look after family and friends, the pollster said. It also found that staff claimed that more interesting work would prevent them taking days off.
The group polled 7500 workers across Europe, including 1005 in the UK, and found that Danes were the least likely to feign illness to get time off work.
Only 4% said they fabricated illnesses for their last day off, compared with 21% of those in the UK.
Peter Abelskamp, of Aon Consulting said: "These are probably conservative figures, considering the number of people who do not admit to faking sickness."
"Employers would be well advised to tackle the issues of sickness and workplace absence head-on, as these seriously impact efficiency and hit their balance sheets."
A recent poll by the CBI found that the average UK worker took 6.4 days off through sickness last year, the lowest number since 1987.