Since leukemia is always fatal, the mortality rates are a reasonably accurate reflection of the occurrence of the disease at various ages. Certain features about the occurrence of leukemia were analyzed from the Vital Statistics of the United States over a twenty year period with special reference to age. A comparison of the occurrence (mortality) during this time has shown a considerable and progressive increase in incidence in persons over 50 years of age from 1930 to 1949. In ages under 50 years the increase was apparently slight but not remarkable.

In addition a comparison of the clinical occurrence of patients with the chronic forms of leukemia has shown that, in recent years, the proportion of patients over 50 years of age is twice as great as in similar groups of patients observed some twenty years previously.

The evidence strongly suggests that the occurrence of leukemia in persons over 50 years of age is actually increasing.