The National Institute of Child Health and Human Development (NICHD) has developed a five-year research plan to gain information about the causes and pathophysiology of sudden infant death syndrome (SIDS) and to develop effective therapeutic and preventive strategies for infants at risk for SIDS. On June 20, 1989, NICHD convened an expert panel to (1) review the scientific knowledge that has been gained in the last 20 years regarding SIDS and (2) determine whether progress has been sufficient to warrant revision of current criteria for SIDS diagnosis, particularly for cases used in research on SIDS. The expert panel, chaired by Dr. L. Stanley James (Columbia-Presbyterian Hospital), was also charged with determining whether subsets of SIDS cases used for research purposes could be defined on the basis of common characteristics.