In Plaid Cymru's manifesto, it said that in Wales, "waiting times for diagnosis and treatment are the worst in the UK".
And the Conservatives have long criticised Welsh Labour's record of running the NHS.
In Wales, Labour has been in power since 1999 - as long as the Welsh Assembly has existed.
But is the health service in Wales really lagging behind?
It's not easy to directly compare the performance of the four health services in the UK.
There are slightly different targets and some outcomes are measured differently - in fact, there is almost no data that is comparable between all four health services.
And, perhaps more crucially, the populations are different.
Wales has the most deprived population in the UK and that has an impact on demand and the cost of running a health service. It also has an older population than England.
Wales is doing worse than England and Scotland at hitting the target of admitting, transferring or discharging patients within four hours of arriving in A&E.
The health service has a different target on waiting times for non-emergency treatment to England and Scotland, but it is doing worse at meeting its own target.
During 2016, Welsh patients waited more than twice as long as those in England for some major surgeries while the diagnosis of pneumonia took nearly two weeks longer and diagnosis of heart disease took eight days longer.
There were minimal or no differences in the waits for the diagnoses of cancer and head injuries and there were shorter waits in Wales than in England for heart bypass and kidney surgery.
But Wales doesn't have the same problem with delayed discharges from hospital as the NHS in England.
Experts have pointed out that NHS Wales had different priorities to its English equivalent, with more emphasis on prevention, public health and social care, but a less "ferocious" focus on meeting targets.
Since around 2010, in the aftermath of the recession and through the policy of austerity, all UK regions have had to make cuts.
In 2009-10, Wales spent the second highest amount per person on health of the four UK nations, behind Scotland. However, subsequent annual decreases over the following three years meant that by 2013-14 it had the lowest health expenditure per head of the four UK regions.
Wales has what are called devolved powers over health spending. That means the Welsh government can decide what it is going to spend regionally on health and education among other things.
But it's important to remember that a large part of the overall money in its coffers is still determined in Westminster.
The budget available to the Welsh Assembly from Westminster under the Barnett formula fell from about £15bn in 2011-12 to a planned spend of about £14bn in 2016-17. The power it has as a devolved administration is in deciding where these cuts should fall.
The earlier fall in health spending was also down to Welsh government decisions, however.
While in England, spending on the NHS had been protected, in Wales, health spending was cut in real terms by 4.3% between 2009-10 and 2012-13, although money is now being put back into health.
But when it comes to social care, the picture is reversed as England has cut government grants to local authorities, resulting in a 16% reduction in funding for social care, while in Wales, local authority spending has been comparatively protected, although, again this is changing.
Even though in Wales, social care spending was better protected, the growing over-65 population means that spending per person has still fallen.