90-day Reporting
But wait, there's more!
If you have been in Thailand for 90 consecutive days, you must report to the Immigrations office.
If you leave and re-enter the country, because you "report your address" on the TM.6 arrival card, the 90-day calendar re-starts on the date you re-enter Thailand. i.e. You only have to report to the Immigrations office if you stay continuously in Thailand for 90 days. Be mindful that the date you re-enter Thailand is counted as day #1.
There is also a procedure at some locations to do the 90-day report via mail.
If you run afoul of the 90-day report, "Any Aliens who fails to comply will be punish with a fine not exceeding 5,000 baht and with an additional fine not exceeding 200 baht for each day which passes.