Oysters that were harvested in Alaska and served on a cruise ship during four separate cruises were implicated in an outbreak of Vibrio parahaemolyticus. The genetic strain of Vibrio that had been isolated from the ill persons matched the strain that was isolated from the oysters. Prior to 2004, Alaskan waters were thought to be too cold to support levels of Vibrio parahaemolyticus high enough to cause disease. This investigation extended by 1000 kilometers the northernmost documented source of oysters that can cause this illness. Rising temperatures of ocean water appeared to have contributed to the outbreak. Vibrio parahaemolyticus was found in oysters collected from the oyster farm that provided the oysters for the cruises.