O' Brien, 39, died on May 1 while descending from Camp I to Base Camp.. According to a communiqué published by the Ministry of Culture, Tourism and Civil Aviation of Nepal on May 3, 2005, he was one of the climbers of the seven-member team of 'International Everest Parivar Expedition 2005' led by Dan Mazur.
Michael O'Brien and his brother Christopher O'Brien wanted to become the first American Brother duo to climb to the top of Mount Everest. They were climbing Mt. Everest to raise money for a foundation devoted to hereditary disease.