From the UK in Turkey
Changes to SGK regulations:
It is no longer compulsory for foreign nationals to join the SGK health scheme. Those wishing to join may do so after one year of residency in Turkey with a residence permit. All foreign nationals who have been residing longer than a year will also be eligible to apply and payments will start from the date of application. Payments will not be back dated.
The only time when a foreign national will be able to cease membership, or withdraw their application from SGK, is when they decide to leave Turkey to return to their country or if they join an official health scheme (e.g. NHS).
If leaving Turkey on a permanent basis an individual must surrender their residence permit to the Foreigners Police Department and write a letter to their SGK office informing them that they are leaving the country.
On joining an official health scheme a letter proving membership of the scheme must be submitted to the SGK office.