A search of the literature has shown that no one has yet given more than cursory notice to the striking infantilism of hookworm disease. So striking is the phenomenon that authorities have contented themselves with mentioning its existence as a well-known fact. The subject is dismissed with the general statement that hookworm victims are undersized, lack pubic and axillary hair and show other evidences of lack of development. It is the purpose of this paper to report in detail the exact study of the grade of development in a case of hookworm disease and, by contrasting it with other types of infantilism, to endeavor to fix its classification. Personal History.— O. J., a white male, aged 22, from Biloxi, Mississippi, was admitted to the Charity Hospital, April, 1909, for treatment for anemia secondary to hookworm infection. He had ground-itch for the first time when he was 6