What do I need for immigration when I leave Thailand after extending my retirement visa?

When you extend your retirement visa, you do not need to apply for a new visa if you want to leave Thailand. However, you will need a re-entry permit if you wish to return after leaving. You can obtain this permit at your immigration office or at the airport right before departure. The costs are 1000 baht for a single re-entry permit or 3800 baht for a multiple re-entry permit at the immigration office, and slightly higher fees apply at the airport.