As many as 50,000 Welsh employees were on sick leave for a month or more each year between October 2010 and September 2013, according to new figures.
The Department of Work and Pensions has published the stats as it prepares to launch a new Health and Work service in a bid to prevent sickness absence turning into long-term welfare dependency.
The service aims to help employees who have been on sickness absence for four weeks to return to work and support employers to manage sick absence among their workforce.
Work and Pensions minister Mike Penning said: "More than 130 million years a day are lost to sickness absence in Great Britain, which has a substantial impact on workers, employers and taxpayers.
"As part of the government's long-term economic plan, we are taking action to get people back into work. This is a triple-win. It will mean more people with a job, reduced cost for business, and a more financially secure future for Britain."