Following investigations in 1972-1973 of outbreaks of enteric disease on cruise ships using American ports, a surveillance system was established which required that 24 hours before arrival in port, each ship report the number of persons with diarrheal illness seen by the ship's physician during the cruise. The reported data were found to be reliable; they established a baseline incidence for diarrhea on cruise ships. A significantly high portion of enteric disease outbreaks occurred on vessels that did not pass routine annual or semiannual sanitation inspections. The cruise ship sanitation program, developed with the cooperation of the cruise ship industry and the Centers for Disease Control, appears to have been successful in reducing the overall rate of cruise ship associated outbreaks of enteric illness.