If you live or work in Thailand and have a 12 month visa, being a extended marriage visa or retirement visa then you need to apply for a re-entry permit before you leave Thailand or your Thai visa will be invalidated when you leave.
Note that when you leave Thailand with a work permit or an extended retirement or marriage visa, when you return your work permit and marriage or retirement visa would have been invalidated as you left without a Thai re-entry permit. There are 2 options when it comes to the re-entry permit. There is a single entry and a multiple entry re-entry permit. You need to go to the immigration office in your area and apply for this re-entry permit. It normally takes 1-2 hours to have it issued. Thai Immigration in Bangkok takes about 3 hours to issue a re-entry permit while Thai Immigration in Pattaya normally takes about an hour. This comes down to how busy these offices are when you apply for the permit.
Note Thai Immigration offices in Thailand and see which office you fall under. They will normally confirm via telephone how long it will take and to confirm the cost of the re-entry permit. The fee for it is 1000 Baht for a single entry or 3800 Baht for multiple entry.
Thai Immigration North (Chiang Rai, Mae Hong Song, Chiang Mai)
Thai Immigration Central (Lopburi, Trat, Rayong, Pattaya, Bangkok)
Thai Immigration South (SongKhla, Saturn, Krabi Phuket)
Thai Immigration North East (Udon Thani, Nong Khai, Khon Khaen)
We have listed the areas with examples of which immigration is located where. Click on the bold lettering to get to the full listing for all immigration offices in that region.