Brewster and Cannon reported the first case of Mongolism associated with acquired leukemia in an 11-month-old "predominantly white" boy in 1930.1Since that time no further cases have been published, although there have been three instances of Mongolism in the 21 well-documented reports of congenital leukemia.* Of the 255 children in whom the diagnosis of Mongolism was made at Duke University Hospital in the 25-year period ending December, 1955, there were 4 who developed leukemia. The incidence is much higher than in the general population of leukemics and is reported in the hope that it may help in the general ultimate understanding of leukemia. Report of Cases Case1.—A 10-year-old white girl was first admitted to Duke Hospital in December, 1951, for evaluation and treatment of acute leukemia. The child had been diagnosed as a Mongoloid at the age of 6 weeks by her family physician. This had been