Merthyr Tydfil is one of two British towns with the highest proportion of people claiming incapacity benefit, according to a new report.
Five Welsh areas have high levels of incapacity benefit claims
A total of 20.5% of working age people in Merthyr Tydfil and Easington in County Durham claim the benefit.
Nine other Welsh areas feature in a table of 33 places with the highest percentages of people on the sick.
The Department of Work and Pensions said the number of people on incapacity benefit was starting to fall.
The report was compiled by the left-wing think tank Catalyst and Sheffield Hallam University. The study highlights those areas of Britain where a large proportion of the working population is claiming incapacity benefit.
Merthyr Tydfil is joint top of the league table with 20.5% along with Easington in County Durham.
The two towns, both former centres of the mining industry, top a table of 30 regions in the UK with the highest percentage of those claiming.
Four other area of Wales are also included in the ten areas with the highest percentage of people claiming the support.
They are Blaenau Gwent, Neath Port Talbot, Rhondda Cynon Taff and Caerphilly.
The report's authors claim that planned government reforms to the benefits system will have little impact in these areas unless more jobs are created.
'Specific employment opportunities'
They describe the 1.1m people claiming incapacity benefit as a "missing workforce" who would be in paid work if the jobs existed in their area.
A spokesperson for the Department of Work and Pensions said: "We are committed to helping people who want to work find sustained employment.
"We have specialist advisers working in local communities who are helping people on incapacity benefit find a job that is not only right for them but specific to employment opportunities in the local area.
"We are making headway and after decades of growth the number of people on incapacity benefit is starting to fall."