A ban on smoking in Barnsley hospital's grounds has come into effect from today.
Health bosses say all patients, staff and visitors will be asked not to smoke on or around the site. New signs have been put up around the hospital to encourage people to stub it out.
The introduction of the smoke-free policy comes on the World Health Organisation's World No Tobacco Day.
Smokers who are admitted as patients will be advised that the site is now smokefree.
As part of their treatment, they will be offered nicotine replacement therapy and referred to stop smoking services.
Trust Chief Executive Dr Richard Jenkins said: "Smoking is the single greatest cause of preventable death, disability and illness.
"It is therefore appropriate that we keep the hospital site smokefree and ask people not to smoke on site."