Smoking ban at Cardiff and Vale hospital entrances
Smoking will be banned outside hospital entrances in Cardiff and the Vale of Glamorgan from the start of May.
Patients and staff will only be allowed to smoke in certain areas until a complete ban takes effect in November.
The University Hospital of Wales in Cardiff, and Llandough, near Penarth, are among sites affected by the ban.
The move has been backed by anti-tobacco group ASH Wales and the British Medical Association (BMA) in Wales.
Dr Sharon Hopkins, director of public health for the NHS board, said: "We want to do this through cultural change, not through finger wagging and fines.
"A hospital is no place for smoking and we as a health board have a duty to our staff and patients to lead by example and show that.
"We will be doing all we can to support both those who provide our care, and those we treat, through our cessation services and No Smoking Wales."
The BMA's Dr Richard Lewis said: "Smoking in public places is putting the health of vast numbers of the population at risk and is also placing a huge burden on the National Health Service.
"Patients come to hospitals to be treated. Providing them with a clean air environment can only be of benefit to their comfort and health."
Tanya Buchanan, chief executive of ASH Wales, said: "People expect clinicians and hospital staff to set a good example by doing all they can to discourage smoking and to protect them from the adverse health risks of breathing in second-hand smoke.
"But we need to realise that tobacco is an addiction, just like alcohol addiction, and we need to treat people accordingly.
"It is therefore vital that staff and patients have appropriate help and support available to assist them to quit."
In February the Welsh Assembly Government unveiled plans to reduce smoking levels in Wales from 24% to 16% by 2020, calling on the NHS to take the lead by making its premises smoke-free.