Leaving the EU could damage the NHS if it puts the economy at risk, its chief executive Simon Stevens has warned.
He said he took "very seriously" warnings of possible recession in the event of Brexit, adding that would be "very dangerous" for the service.
"When the British economy sneezes, the NHS catches a cold," he said, adding it would be a "terrible moment" at a time when the NHS needed extra investment.
The Leave camp says a Remain vote would have "huge consequences for the NHS".
Asked about the impact of EU migrants on the health service, Mr Stevens said: "It clearly is the case that where those migrants are paying taxes that is contributing to the revenues that can afford an expanding NHS.
"When the NHS was set up in 1948 we had a population of 50 million - we're at 65 million now - and the NHS has perfectly, successfully coped with a 15 million expansion in our population - provided it is properly resourced from the proceeds of economic growth it can do that."
Mr Stevens also said the NHS "has benefited enormously" from having doctors, nurses and care workers from the EU working within the health service.
There would be an impact if any of those 130,000 staff chose to leave the NHS because of uncertainty over work visas if the UK leaves the EU, he added.
It could also be difficult for the UK to "get the treatments we need at an affordable price" if the pound were affected by Brexit, because many drugs are priced in euro and dollars.
Sunday, 22 May 2016
BBC News: Brexit 'could damage NHS', health boss warns