Patients and visitors will be banned from using electronic cigarettes in hospital grounds across Scotland within weeks.
NHS boards will be required to ensure that their grounds are smoke-free by April.
The Scottish government has said it is up to individual health boards whether they prohibit the use of e-cigarettes.
A survey by BBC Scotland has revealed that all but one health board will completely ban the devices.
Just NHS Lothian will allow the restricted use of the so-called electronic nicotine delivery systems in designated outdoor areas away from entrances.
Other health boards claim that there are concerns about the safety of the devices.
Julie White, chief operating officer NHS Dumfries and Galloway, said: "Our directors of public health across the health boards in Scotland have issued some advice to us which basically states that until we have more evidence available to us around their use and their impact, they should be treated like any other nicotine product and they should not be used in the grounds."
She said the policy could be reviewed if their regulatory position changes.
A spokesman for NHS Greater Glasgow and Clyde also confirmed that e-cigarettes are not permitted as part of their smoke-free policy.
She added: "These products are currently not regulated and there are concerns over potential safety issues with the products. In addition e-cigarettes mimic the habit and look of smoking and therefore provide negative role modelling for young people."
But the move has not been welcomed by anti-smoking health charity ASH Scotland, which claims they can help smokers to quit.
Chief executive Sheila Duffy said: "There is a clear case for hospital grounds to be free from tobacco use, which is always dangerous.
"However e-cigarette policies should not be so restrictive that they discourage smokers from trying an alternative that might help them to move away from tobacco."
Some of the devices are expected to be licensed for medicinal use as nicotine replacement therapy, she said.
Ms Duffy added: "Hospitals might also choose to draw a distinction between devices which look like cigarettes and some new vaping devices, which look nothing like a traditional tobacco cigarette and so don't lead to confusion with smoking."
Simon Clark, director of smokers' group Forest, also criticised the move.
He said: "Many smokers use e-cigs to cut down or quit tobacco so it seems perverse to prohibit their use.
"Banning them is counter-productive because if both products are prohibited there will be no incentive to switch to e-cigarettes. Smokers will simply carry on smoking, ban or no ban."
Under the terms of the Scottish government's tobacco control strategy, all NHS boards must make their entire hospital grounds smoke-free by the end of March.
Many health boards have already implemented the restrictions while others, like NHS Tayside and NHS Lothian, are in the process of removing smoking shelters.
A spokesman for the government said: "It is a matter for boards to decide how they implement and enforce their smoke-free policies, this includes whether they chose to incorporate a ban on e-cigarettes.
"No specific resources have been allocated. However, the Scottish government allocates around £11m a year to NHS Boards for smoking-related services."