The patterns of esophageal cancer are dramatically changing in the United States. Three decades ago the large majority of these cancers were squamous cell carcinomas, but the incidence of esophageal adenocarcinoma has been steadily increasing. By the early 1990s, adenocarcinoma had become the most common cell type of esophageal cancer among white patients, although squamous cell cancers still predominated among black patients. The trends are not simply due to gastric cardia cancers now being called esophageal adenocarcinomas, because the rates of tumors appearing just below the esophageal-gastric junction are also increasing. Tobacco and alcohol consumption are the primary causes of squamous cell carcinomas of the esophagus. The causes of esophageal adenocarcinoma are not well known; thus, reasons for the increasing incidence are not clear. Tobacco smoking has now been established as a risk factor, but there appears to be little link to alcohol consumption. One of the strongest emerging risk factors, however, is obesity. Increases in the prevalence of obesity and the incidence of esophageal adenocarcinoma are parallel, and several epidemiologic studies have shown upwards of threefold excess risks among overweight individuals. Further research into the causes of these usually fatal cancers may help identify other potential determinants and provide needed information to help stem their increase.