Gottlieb MS [Department of Medicine, and Department of Biostatistics and Epidemiology, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA], Carr JK and Morris DT. Cancer and drinking water in Louisiana: colon and rectum. International Journal of Epidemiology 1981, 10: 117–125. A case-control mortality study conducted in 20 parishes (counties) of South Louisiana to determine what relationship drinking Mississippi River water might have on mortality from colon or rectal cancer, found a significant risk for rectal cancer associated with surface water. Rectal and colon cancer deaths (692 and 1167) from 1969 to 1975 were matched to non-cancer deaths by age at death (% 5 years), year of death, sex and race, and within groups of parishes with similar industrial and urban-rural characteristics, each group being defined so as to ensure that it included as nearly as possible equal populations using water from ground and surface sources, based on the 1970 census. Colon cancer did not relate significantly to any water variable, but rectal cancer associated strongly with surface, or Mississippi River, water. The odds ratio for rectal cancer between those who were bom and died on ground water was 2.07 with 95% C.I.: (1.49–2.88). A multi-dimensional contingency table analysis found the association between rectal cancer and surface water significant at the.0001 level and not dependent on age, race, sex or year of death. The risk for men was slightly higher than for women, but both sexes showed an increased risk. Chlorination also associated significantly with rectal cancer. Among those who used river water, the risk increased inversely as the distance from the mouth, with greater risk downstream from the many industries which line the river.