The Centers for Disease Control and Prevention (CDC) provided technical assistance to the Ministry of Health of Haiti during an outbreak of over 100 cases of acute illness and death in the northern region of Haiti during a 4-month period beginning in November 2000. The epidemiologic, clinical, and laboratory findings in this investigation indicated the ingestion of unripe ackee fruit as the most likely cause of this outbreak. This report describes the CDC field investigation in Haiti and gives a brief overview of the current state of knowledge about ackee poisoning.