Summary In an outbreak of epidemic diarrhea of the newborn involving sixty-three infants, there were fifteen deaths. The incidence of the disease and the death rate were higher among the premature infants. In eleven instances a biphasic clinical course was encountered, in which after clinical and biochemical improvement there suddenly developed ominous symptoms with a state of collapse and death for eight of the infants. Control of the outbreak was not obtained until the entire department was closed to admissions and thoroughly cleaned before it was reoccupied. An etiologic bacterial agent was not discovered, and virologic studies could not be performed. Therapeutic measures included maintenance of hydration, correction ofacidosis, modification of feeding, and administration of amino acid solution, plasma, and whole blood. Neither sulfonamide nor penicillin therapy seemed to influence the clinical course of epidemic diarrhea of the newborn, and in a limited series the intramuscular administration of gamma globulin had no apparent prophylactic or therapeutic effect.