A total of 2,298 dehydrated infants, among 9,674 infants admitted to Emergency Unit and Intensive Care Unit of Clinica Infantil "La Paz" between 1970--1974 are analyzed. The annual incidence of the different types of hypotonic, hypertonic and isotonic dehydration is studied. The peculiarities of the data are discussed and compared with those described by other authors. High incidence of hypertonic dehydration (25.4%) is emphasized.