Mona Island, located nearly halfway between La Hispaniola and PR, is considered a unique and pristine natural wonder in the Caribbean. Its coral reef ecosystems are paramount for maintaining the meta-population connectivity of most commercially important fish species in the region. But an unprecedented sea surface warming event occurred during 2005 throughout the northeastern Caribbean Sea that caused a mass regional coral bleaching event. It was followed by significant coral mortality. This study is the result of an exploratory expedition carried out in June 2006 by Sociedad Ambiente Marino and the UPR-Coral Reef Research Group to conduct a rapid ecological assessment to address what was the impact of the bleaching and coral mortality event in Mona Island. Digital video-imaging was used to document the status of benthic community structure at six locations. Coral reefs were characterized by a dramatic phase shift favoring macroalgal-cyanobacterial dominance. Percent coral cover ranged from 3 to 14%, when estimates conducted between 1981 and 2000 showed % coral cover values ranging from 10 to 35%. Percent macroalgal cover ranged from 42 to 85%, often dominated by unpalatable brown algae, Dictyota spp. Percent cyanobacterial cover ranged from 0.3 to 13%. Most large reef-building coral species were showing significant signs of mortality. There was also a significant difference (p=0.0002) in community structure among sites, which were clustered in four different patterns according to degree of mortality and post-mortality trajectory. Differences were actually attributed to the high frequency of other benthic categories such as recently dead corals (RDC), crustose coralline algae(CCA) and rubble (SPR). This is the first known mass coral mortality event reported in Mona Island and represents an unequivocal sign of climate change impacts.