Scottish Government advice is for all those travelling to the islands to take two Covid-19 tests – one three days before travel and one on the day of travel. Rapid lateral flow tests are now freely available to order for anyone without symptoms.
The advice comes as the bank holiday weekend will be the first opportunity for many tourists to visit the islands, after restrictions around accommodation eased on Monday.
Most island areas have been in level three restrictions throughout the winter, with the exception of Skye.
NHS Highland has seen low rates of Covid-19, while Orkney has had just one case in the past month, and Shetland has had none.
The Western Isles have now passed a month with no new cases, after a rise in the new year.
More than 50 cases were linked to an outbreak on the Isle of Barra in January, while 90 were linked to a later outbreak on Lewis.
The Western Isles were placed into level four lockdown at the end of January, measures which were only lifted on March 23.
Gordon Jamieson, chief executive of NHS Western Isles, urged visitors to do their utmost to avoid bringing the virus back to the now Covid-free area.
“Anything that reduces the risk of coronavirus being brought into island communities by people who are unaware they are infectious is welcomed,” he said.
"We would strongly encourage anyone planning on travelling to our islands to participate in this scheme to help protect the Western Isles and our vulnerable systems.”
Dr Tim Allison, director of public health at NHS Highland, urged visitors to protect island communities by taking a test before visiting.
He said: “It is understandable that people will want to travel across the country to see loved ones now that travel restrictions have been lifted, but it is absolutely vital that we continue to observe social distancing, wash our hands and wear face masks when indoors.
"It is also important that those with any symptoms of Covid-19 do not travel and self-isolate immediately.”