In the Department of Obstetrics and Gynecology of the University of Chicago from Oct. 1, 1934, until April 1, 1940, we have had the opportunity of examining at autopsy more than 2,500 fetuses and infants of varying gestational age and extra-uterine age up to 1 year. This has in part been made possible by the cooperation of Dr. Herman Bundesen, president of the Chicago Board of Health. The present report is based on 2,000 autopsies which comprise the entire group with the exclusion of the fetuses classed as abortions,1the infants over 1 month of age and those in which adequate maternal and infant histories were unavailable. Six hundred and eight of the fetuses and infants were born and died at the Chicago Lying-in Hospital, 895 were sent to us for autopsy, and 497 were examined at autopsy elsewhere by Dr. Aaron Günther for the Chicago Board of Health and tissues sent to us for microscopic examination. In each case a complete autopsy including examination of the head was performed and tissues were subjected to microscopic study.