It has been shown that hypernatremia may accompany dehydration in infants with diarrhea and with infections associated with interference with water intake. Suitable modification of the treatment dehydration for these patients has appeared to improve the results of their care. Hypernatremic dehydration may be suspected from the history and clinical features and is readily diagnosed by laboratory procedures. The occurrence of neurological manifestations, some of which may be irreversible, is a feature of outstanding importance. Despite loss of body water the usual changes in tissue turgor and the circulatory state associated with severe dehydration may not be present. Because in this type of dehydration, a large intracellular water deficit exists, the repair solution should be relatively dilute with respect to sodium. The best results have been obtained by administering fluids which, if combined, would have a final sodium concentration of from 15 to 40 mEq./l. Hypocalcemia has been a frequent complication and more study is needed to elucidate its pathogenesis. Awareness of its occurrence facilitates therapy. As in other types of dehydration in infants, the potassium deficit may be impressive and should be corrected promptly after restoration of renal function. The somewhat special treatment indicated for patients with hypernatremic dehydration makes recognition important. Recognition or suspicion from clinical signs and rapid laboratory diagnosis are essential for optimal management.