A Royal Thai Navy helicopter carried the two sick divers and the body of the third diver back to Phuket.
First reports said the two divers confined in the decompression chamber at Vachira Phuket Hospital in Phuket City were not in good shape.
The dead diver was named as Sudhat Sokpok, 45. The divers who required decompression were Suwat Julapong, a Professor at Prince of Songkhla University, and Royal Thai Navy Petty Officer First Class Patopong Japimai.
The two sick divers, initially bleeding from the mouth, were in the chamber in Phuket City for six hours and have now come out, a spokesperson for the hospital said tonight.
''We believe they will make a full recovery,'' she said.
It's reported that problems arose today when divers sought to shift a mooring buoy where the anchor had drifted to a depth of 42 metres - well beyond the limit of most amateur divers.
Scores of Thai and foreign divers are said to have joined a project that aimed to fix or replace buoys around the Similans, one of the favorite destinations for divers visiting Phuket and neighboring Phang Nga province.
The tragedy came as one group of volunteers tried to adjust buoys around Koh See (Island Four).
The man who died was a veteran Thai diver who has totted up between 500-600 dives. He was a businessman from Songkhla province.
One professional diver who spoke to Phuketwan tonight said that volunteers should not be used to adjust moorings at such depths.
''It appears to be a money-saving exercise on the part of the national park officials,'' he said. ''Professional divers should be employed to fix the moorings over a long period of time.
''Instead it has become a community project and clearly, people are being asked to dive beyond their capacity.''
Police from Phang Nga are investigating the death.
The Similans are well-known to thousands of snorkelling day trippers and liveaboard divers who usually stay on Phuket or in Khao Lak and reach the islands via Tablamu pier in Phang Nga.