The four most important deficiency diseases in developing countries today are protein-energy malnutrition (PEM), xerophthalmia, nutritional anemia, and iodine deficiency disorders. Control of these nutritional diseases requires systematic diagnosis of the existing situation and appropriate intervention strategies such as targeted food and specific micronutrient supplementation, food fortification, nutrition education, and reductions in infections as well as general improvements in economic conditions and social equity. Iodine deficiency is the leading cause of preventable intellectual impairment and is associated with a spectrum of neurological and developmental pathology. More than one billion people are at risk. The technology of iodine deficiency intervention is well established. Iodized salt, the preferred method, is easy to produce, administer in physiologic doses, and is cost effective.