Does a holder of a Non-Immigrant O-A Visa (Multiple Entry) need a Re-Entry Permit if he leave Thailand and want return? 

A re-entry permit is not required if you Non-OA visa is still valid. If you enter before it expires you will get a new one year entry.

If expired you would need a re-entry to keep the remainder of the permit to stay valid that you got from your last entry to the country valid when you enter the country.

 

Look at your Visa for the Enter By date - that is when your OA Visa will expire. As mentioned, until that date you can reenter Thailand without needing a Re-Entry permit and receive another one year permitted stay.  However, if you plan to return after that date, you will need a Re-Entry Permit to keep your current permission to stay date "alive."  The Re-Entry Permit will expire on the date your current permission to stay expires.

7 hours ago, ubonjoe said:

A re-entry permit is not required if you Non-OA visa is still valid. If you enter before it expires you will get a new one year entry.

If expired you would need a re-entry to keep the remainder of the permit to stay valid that you got from your last entry to the country valid when you enter the country.

 

I have used the re-entry permit with O-A visa for years but what effect does the required health insurance have on this ?  Suppose I enter with new O-A and return to USA after 7 months ?  At this point only 5 months is left on the insurance. Do I still get my 12 months when I buy re-entry permit at airport on the way out ? If not is there a workaround ?  Thanks.

3 hours ago, Searat7 said:

I have used the re-entry permit with O-A visa for years but what effect does the required health insurance have on this ?  Suppose I enter with new O-A and return to USA after 7 months ?  At this point only 5 months is left on the insurance. Do I still get my 12 months when I buy re-entry permit at airport on the way out ? If not is there a workaround ?  Thanks.

If you have a re-entry permit (and the immigration official does not ignore it) then you will be stamped in until the date specified on the re-entry permit (the expiry date of the associated permission to stay). If you still have an unexpired O-A visa, the official might well decide to ignore the re-entry permit, and stamp you in on the visa instead, giving you a full 12 months. As you implied, immigration will probably insist that you have health insurance (not Covid insurance) to cover the full 12 months in that case.