A July to September outbreak of Vibrio parahaemolyticus infections was found to be associated with consumption of raw oysters and clams harvested in Long Island Sound. The New York City Department of Health (NYCDOH) began investigating when a New York City resident was diagnosed with toxigenic V. cholerae O1 infection. The NYCDOH found no other V. cholerae infections, but noticed a cluster of V. parahaemolyticus cases among residents of Connecticut, New Jersey and New York with dates of onset between July 21 and September 17. Questionnaires on food history found that 22 of the 23 culture-confirmed cases had eaten or handled oyster, clams, or crustaceans. Traceback found that the oysters and clams came from Oyster Bay, Long Island Sound. Those who had eaten these oysters or clams had V. parahaemolyticus matching PFGE DNA fingerprints.