Smoking has been banned in the grounds of Leeds hospitals, with people urged not to be rude to staff trying to implement the new rules.
The smoking ban, which came into force on Tuesday, covers several sites including Leeds General Infirmary, St James's and Leeds Children's Hospital.
Leeds Teaching Hospitals NHS Trust said it was an important part of its public health strategy.
Some people, however, have questioned how it will be policed.
Writing on Twitter, Rosie Wilson said: "Didn't stop the smokers outside Lincoln wing today!
"Who's going to police it because I'm not approaching people to tell them.. seen enough incidents outside there over the years!!"
It comes after a plea from the trust not to abuse staff who try to enforce the ban.
It said: "Please do not be rude to our staff if they ask you not to smoke.
"They do it because they care and we're trying to maintain an environment that supports everyone's health."
David Berridge, Deputy Chief Medical Officer at Leeds Teaching Hospitals NHS Trust said: "It's taken lot of preparation with our local partners and with all our staff to get us to the point of becoming a fully smoke-free trust - thank you to everyone involved.
He added: "This is an important part of our public health strategy and we are committed to becoming a smoke-free hospital in 2020, in line with NICE Public Health guidance.
"We're proud to be taking this step and we know other NHS trusts are implementing plans to become smoke-free."
The NHS Trust said 15.3% of adults in the Leeds area still smoke and tobacco use remains the single largest cause of health inequalities and premature death.