NCI investigators are collaborating with the International Agency for Research on Cancer (IARC) and the Digestive Disease Research Center of Tehran University of Medical Sciences to study the etiology of esophageal squamous cell carcinoma in Golestan Province in northeastern Iran, which has some of the highest rates of this cancer in the world. A case-control study, Gastric and Esophageal Malignancies in Northern Iran (GEMINI), with 300 cases, 571 neighborhood controls, and 300 clinic controls, has recently completed accrual; all participants will be interviewed and undergo collection of biological specimens including blood, hair and nails. Atrak Clinic, a referral clinic for upper gastrointestinal diseases, serves as the field center for the study.