it's on Koh Phangan in Thailand, a 40 minute boat ride from Koh Samui. it sounds like a great beach party (and many swear it is) but the experience is fraught with danger. You need to take some precautions if you want to survive.
Here's our take on the party.
http://journals.worldnomads.com/safetyhub/story/66535/Thailand/Full-Moon-Mayhem-Surviving-the-Party almost 9 years ago
Koh Phangan is the place, i went once and it was crazy mad ! its like New Years eve x 10.
Anyway do it but be very very careful if your a women, stay away from friendly strangers and don't touch drugs or be around people that are doing them.
I get good deals on hotels here http://www.kohphanganhotels247.com/ almost 9 years ago