Striking Western Isles doctors will only attend emergencies or urgent cases during 24 hours of industrial action on Thursday.
The one-day strike is over a dispute over national NHS changes to the pension scheme.
NHS Western Isles says all emergency services and core clinical services will continue as normal. This includes critical treatments such as for cancer, renal dialysis, emergency mental health and maternity services.
Striking doctors are not walking out - they will turn up at their place of for work and attend to people needing urgent treatment. But non-urgent and routine cases will be postponed.
Not all doctors are taking part in the strike. The health board says it will check which patients will be disrupted and reschedule their appointments.
However, patients can directly check if they will be disrupted by calling the contact telephone number on their hospital appointment letter.
All GP surgeries will respond to urgent appointments and the majority will be running as normal for routine appointments.
Gordon Jamieson, Chief Executive for NHS Western Isles said: "While we acknowledge the right of colleagues to take industrial action, we would like to reassure patients and the wider public that safe and effective care remains our priority.
"Should there be any disruption to planned appointments, patients will be contacted in advance to advise them of arrangements. Otherwise patients should attend appointments as planned."