The environmental factors latitude, temperature, and water consumption have been correlatedwithcancerincidencerates. To date, there is noconsensus of opinion that explains how these environmental factors alter the incidence of cancer. A fluoride belt stretches across the north and east of Africa, through the Middle East, across Pakistan and India, into Southeast Asia, and the south of China. There appears to be an association between areas with low cancer incidence rates and high fluoride concentrations in the water supply. This ecologic study attempts to determine if fluoride is correlated with cancer incidence rates. If so, this study also attempts to determine whether fluoride is a factor in the correlation between latitude, temperature, and cancer incidence rates. Population groups with very high cancer incidence rates and population groups with very low cancer incidence rates are compared to identify environmental factors that might explain the correlation between cancer incidence rates and the environmental factors of latitude, temperature, and fluoride. There is a positive correlation between cancer incidence rates and latitude (r = 0.71). There is an inverse correlation between cancer incidence rates and temperature (r = -0.87). There is also an inverse correlation between cancer incidence rates and fluoride concentration in the drinking water (r = -0.75). Very low cancer incidence was found in areas with high fluoride concentrations in the drinking water.