There are two major issues in the epidemiology of Hodgkin's disease today. The first concerns the reason for the extreme heterogeneity of persons affected with the disease. There is evidence to support the idea that Hodgkin's disease is, in fact, at least two processes, each with a distinct etiology. However, the possibility remains that the heterogeneity results from variations in host response to a single etiologic factor. The second issue concerns specific etiologies of the disease. There is some evidence that the disease among young adults has a virus etiology. However, there is also evidence contrary to this hypothesis. The disease among the elderly remains a complete enigma.