A peculiar destructive granulomatous lesion of bone was first recognized and described independently in 1940 by Otani and Ehrlich (18) and Lichtenstein and Jaffe (14). Lesions of similar type had previously been described by Finzi (6) in 1929, Mignon (16) in 1930, and Schairer (21) in 1938. They did not, however, consider the lesion to be a distinct entity and referred to it as myeloma with prevalence of eosinophils, granulation tumor of bone, and osteomyelitis with eosinophilic reaction, respectively. Lichtenstein and Jaffe's denomination, “eosinophilic granuloma of bone,” has been widely accepted. Up to July 1, 1945, 48 acceptable cases were recorded in the literature. To these are added the 5 reported in this paper, making a total of 53 published cases. Etiology The cause of eosinophilic granuloma of bone is as yet unknown. Trauma has been considered significant, but proof of a causative relationship is lacking in most instances. Ziehl-Neelsen stains and guinea-pig inoculation of material from the lesi...