From January 1995 through July 1998, we investigated the occurrence of Cyclospora cayetanensis infection associated with gastrointestinal illness or diarrhea in foreign residents and natives of West Java, Indonesia. We found that C. cayetanensis was the main protozoal cause of gastrointestinal illness and diarrhea in adult foreign residents during the wet season. The parasite rarely caused illness in the indigenous population or in children.