North of Iran is part of the "Asian esophageal cancer belt", which has some of the highest rates of esophageal cancer (EC) in the world. The earliest reports of this high incidence date back to the early 1970s, when a population-based cancer registry was established as a joint effort between Tehran University and the International Agency for Research on Cancer (IARC). This registry confirmed the high incidence of EC (age-standardized incidence rates of 109/100,000 in men and 175/100,000 in women) in the eastern portion of the Caspian Sea littoral, presently known as Golestan Province. A collaboration was formed in 1995 between Digestive Disease Research Institute of Tehran University of Medical Sciences, National Cancer Institute, and IARC to study EC and the determinants of its high risk in these parts of Iran. This collaboration has since expanded to include other international collaborators, and to answer many more health topics, such as cardiovascular disease, lifestyle, and mortality.