The possible causes of hypochromic anemia were sought in a study of 272 infants whose blood had been found to contain less than 9 Gm. of hemoglobin per 100 cc. The most common factor was prematurity or a birth weight of less than 3,000 Gm. Prematurity was present in 80% of the patients with a hemoglobin concentration of less than 5 Gm. per 100 cc. The incidence of severe hypochromic anemia in infants weighing more than 4,000 Gm. is extremely low. A first child was less liable to become anemic than were later siblings; single children were less liable than twins; and girls less liable than boys. Dietary information was incomplete, but the most frequent dietary pattern, before treatment, was found to have been two quarts of milk daily, supplemented with mashed potatoes, dried beans, crackers, or bread. The evidence showed, however, that deficient iron intake was not the sole cause of severe hypochromic anemias. Prevention therefore depends largely on the recognition of susceptible infants in the population. These should be watched carefully and treated prophylactically with adequate doses of medicinal iron.