Sudden unexpected death in infancy, long a subject of interest, has assumed greater statistical significance with the steady decline in deaths from other recognized causes in infancy. This is attested to by the increasing frequency with which articles on the subject of sudden unexpected death are encountered in the medical literature.1-14Theories purporting to explain the phenomenon of sudden death are almost as numerous as the articles. In general, they may be divided into two groups: those based upon observations in a few cases and which are not applicable to a large series and those based upon minor tissue alterations commonly found at autopsy, the importance of which has not been supported by clinical observations or bacteriologic or virologic investigations. The present study was undertaken in order to evaluate the information that could be gained purely from autopsy materials. Source of Material At the Armed Forces Institute of Pathology