THE OCCURRENCE of multiple cases of leukemia within a single family has often been sufficiently striking to merit a published report by the clinician who encountered it. An excellent review of such cases has been made by Videbaek,1 who has summarized 26 "incontrovertible" cases in the literature up to 1947 and has added 13 cases of his own. The family to be described in the present report is unique in several respects. It is the first reported with leukemia in more than three siblings, and it represents an easily studied group, for all affected members have been examined and treated in the University of Minnesota Hospitals within the last 14 years. CLINICAL MATERIAL The pedigree of the "S." family is shown in the figure. Only the near relatives are included, and the affected persons are indicated by solid symbols. There have been no consanguineous marriages. This pedigree has not been