Addenbrooke's Hospital in Cambridge has implemented a total smoking ban to encourage healthier lifestyles.
Staff, visitors and patients won't be able to smoke anywhere on site - and there's no longer any outdoor smoking areas.
It also applies to the Rosie Maternity Hospital.
The Trust's Chief Executive Dr Keith McNeil says it's in accordance with national guidelines that hospitals should be smoke free.
"It sends a message that we're not just about treating people here, we want society as a whole to be healthier," he said.
"It's very important from that point of view that we don't condone smoking on the site anywhere."
More top news
It's going to stay mainly dry and sunny this afternoon. Just the chance of the odd isolated shower in places. Highs of 28 degrees
A severely disabled baby should be allowed to die - despite protests from his parents, a High Court judge has ruled.
A fine day with plenty of sunshine, especially at first. Staying dry for most, although some cloud will build during the afternoon.