New figures show that one in five patients in Wales are waiting longer than 26 weeks for treatment on the NHS.
Although just 4 percent of patients in England have to wait 6 months or more for treatment while in Scotland that figure is just 2 percent.
A freedom of information request by Plaid Cymru found that while around 97 percent of Scottish and English patients are treated within six months, the figure in Wales plummets to well under 80 percent.
Plaid Cymru's Shadow Minister of Health Elin Jones said:
Plaid Cymru have now called on the Welsh Government to recruit another 1,000 doctors to create a 'sustainable NHS'. Wales has one of the lowest levels of doctors per head of the population in the EU with only Romania and Poland worse off.