Irons leaves behind a pregnant wife, Lyndie, and younger brother, Bruce, who is a former World Tour competitor.
Irons died in Dallas during a layover while between flights from Puerto Rico to his home in Hawaii. His body was discovered in a hotel room Tuesday morning, after he failed to respond to a wake-up call.
He had been ill and was said to have contracted dengue fever, but investigators found sleeping pills and anti-depressants in his room. An autopsy was performed Wednesday and lab results might become available Friday.
Irons, who was raised on Kauai, withdrew from the Rip Curl Search Puerto Rico on Sunday. He cited an illness contracted during a previous competition in Portugal.
Irons was known for his fast but fluid style on a surfboard, and for his epic heat battles with Kelly Slater, many of which occurred as Irons was reeling off his titles in succession from 2002-04.
Irons also was a dominant force in Hawaii, where he won four prestigious Vans Triple Crown of Surfing titles and four Billabong Pipeline Masters championships. The Triple Crown is scheduled to begin next week.
Irons' death comes at a time when Slater, 38, pro surfing's most accomplished athlete, is in Puerto Rico trying to clinch a tenth world title.
Irons had his ups and downs after his title run and often struggled. He took last year off, citing personal reasons, but being married seemed to give him new inspiration. He returned to the tour this season and is presently ranked No. 16 in the world.
Irons' wife is scheduled to give birth to the couple's first child, a son, in December.
-- Pete Thomas
Editor's note: A similar version of this post is on the GrindTv.com surf and outdoor blogs