The hypothesis that Hodgkin's disease encompasses at least two ætiologically distinct entities with differing age-distributions led to an examination of the regional variation of mortality by age within the United States. A region comprising eleven contiguous Southern states is of particular interest, in that, while it exhibits mortality among the middle-aged and elderly comparable to that in the rest of the United States, mortality among young adults is only about half that observed in the remainder of the country. This pattern was seen for both sexes and in two separate time periods. It is interpreted as supporting the " two-disease " hypothesis. Differences between the two areas in the sex ratios of mortality from Hodgkin's disease among the young strengthen the interpretation.