The occurrence of pneumonia in newborn infants has been recognized by pathologists for many years. The authors are of the opinion that pediatricians have not recognized this condition as often as they should and that early diagnosis will permit successful treatment. The authors refer to a form of pneumonia which may develop in utero or in the first few hours of life in contrast to the forms of pneumonia well known to occur later in the neonatal period from a variety of established etiologic agents. The organisms found in the pulmonary inflammation in the fetal lung usually are those commonly found in the maternal vagina. The pathogenic mechanisms which permit these organisms to invade the fetal lung are discussed. Pneumonia in the early neonatal period usually occurs in cases where membranes rupture more than 6 hours before delivery, who were the products of prolonged and complicated labors, or in premature infants. Details of treatment to be instituted in newborn infants demonstrating signs indicative of pneumonia are discussed. The authors suggest that pneumonia is a sole cause of death in 6 to 9 per cent of all stillborn or newborn infants. Infants affected with pneumonia at birth commonly show signs of illness such as would be expected from pneumonia, although the manifestations may be subtle and all the usual symptoms and signs are not regularly present. The authors state that if pediatricians were to be suspicious of the diagnosis of pneumonia in the newborn and observe the symptoms described, the diagnosis would be made more frequently and successful therapy might be instituted. They also have hopes that some cases might be prevented by remembering the conditions during the later stages of pregnancy which may result in pneumonia in the fetus.