The prevalence of the Sudden Infant Death Syndrome (SIDS) has dropped in most countries following the development of education campaigns on the avoidance of preventable risk factors for SIDS. These include factors in the infant's micro environment, such as prenatal passive smoking, administration of sedative drugs, prone sleep, high ambient temperature or sleeping with the face covered. Sleep laboratory studies have shown that these risk conditions contribute to the development of respiratory and autonomic disorders and reduce the child's arousability. The opposite effects were seen when studying factors protective from SIDS, such as breastfeeding or the use of a pacifier. In victims of SIDS, similar breathing, autonomic and arousal characteristics were recorded days or weeks before their death. It is concluded that in some infants, already immature control mechanisms can be aggravated by environmental factors.