Initially I was under the impression that we would not have to clear customs coming back from STT (St. Thomas), since it is a U.S. territory. Then my guidebooks (Fodor's and Frommer's) give the impression that you DO have to clear customs (without actually spelling it out in so many words). Since you do have a duty-free allowance, this would also lead me to believe that the only way to enforce the allowance would be to make people clear customs. However, AA tells me that I do not have to clear customs upon return to MIA (I was concerned since the connection time is only 50 minutes).

Now I am really confused. Do I or don't I have to clear customs when returning from STT (I am a U.S. citizen)?

Yes, you do have to clear customs and immigration when departing STT for either the US Mainland or Puerto Rico. They will enforce the duty free allowance at that point. Once you arrive in MIA you will not need to clear customs or immigration.

http://www.flyertalk.com/airports/ftairports_forum/Forum11/HTML/000046.html

Thanks, that clears things up for me!

Bumping this up as I couldn't find any search with an answer. I will be going down to SJU from EWR. My return flight is SJU-STT-EWR. I have 2 questions, -#1 Will I have to clear customs in STT even though I'm transiting from SJU (I am a US Citizen) and #2- Regarding Duty Free purchases, I usually buy a couple of bottles of rum in SJU. As I've never been to STT, should I wait and make my purchases there or as I'm just in transit, will I not be able to buy any duty free in STT (or can I buy in both ???). Thanks !