An estimated 4500 cases of V. parahaemolyticus infection occur each year in the United States. However, the number of cases reported to CDC is much lower because surveillance is complicated by underreporting. Laboratories rarely use the selective medium that is necessary to identify this organism, and it is likely that many cases are undetected. To improve our ability to monitor trends, infections caused by V. parahaemolyticus and other Vibrio species became nationally notifiable in 2007. State health departments report cases to CDC, and these reports are summarized annually.