"Downhill esophageal varices", classically defined as those that develop in the upper region of the esophagus, are less common than the "uphill" type, which is usually produced by portal hypertension. Various causes of downhill varices have been reported, but mediastinal tumor is the most common responsible lesion. Castleman's disease, or angiofollicular lymph node hyperplasia, is a rare pathological process of unknown etiology that usually develops in the mediastinum. We report the case of a 60-year-old woman whose large esophageal varices were detected incidentally. The cause was a mediastinal mass which was diagnosed as Castleman's disease on histopathological examination of a surgical specimen. This patient's varices most likely formed as a result of copious blood drainage from the tumor into the esophageal veins. Evidence for this was the lack of the classic downhill pattern, the absence of superior vena cava obstruction, and the fact that the varices resolved after the tumor was removed. It is our opinion that this type of varices should be renamed, and we suggest that "overflow varices" would be an appropriate term.