An accidental spill of phenol (100%) into the Nakdong river with subsequent contamination of the tap water for about two million consumers in Teagu city of Korea occurred in March 1991. A historical cohort study of 6,913 individuals was undertaken to determine association with illness. Population subjects were divided into two groups of exposed and unexposed. Exposed subjects were reported to have significantly more phenol associated symptoms than those in a nearby unexposed area (39.6% vs. 9.4%, p < 0.01). Especially, in the related symptoms, highly significant differences were noted in the number of subjects reporting gastrointestinal illness such as nausea, vomiting, diarrhea, or abdominal pain. During the accident, study subjects who experienced peculiar taste or odor in the tap water were significantly more in the exposed areas (92% vs. 34.3%).