The causes of SIDS are unknown, and there are no tests that predict which infants will die of SIDS. Home monitoring, while it may prevent death in some high-risk infant populations, has not altered the overall incidence of SIDS. Studies have identified several important risk factors, such as prematurity, low birth-weight, inadequate prenatal care, maternal smoking, maternal anemia, and poor socioeconomic conditions. Other recent studies have raised important questions about child care practices, such as infant sleeping position. Still others raise equally important questions about the role of neglect or intentional injury, which now must become the subject of proper scientific investigation. The possibility that underlying metabolic defects may account for a substantial proportion of cases has been raised but requires verification. A common thread is evident: There are risk factors, such as maternal smoking and infant sleeping position, that could be subject to preventive intervention strategies.