Despite the well-recognized advantages of breast-feeding to both mother and child, malnutrition of breast-fed infants can occur. We report two cases of breast-fed infants with cachexia, hypernatremia, and, in the one case in which it was measured, an elevated level of breast-milk sodium. These cases, along with several reported previously, emphasize the need for proper education and close and early follow-up of the nursing mother and infant, especially since a lack of parental awareness can be part of this syndrome.