In the last decade there have been major reductions in the sudden infant death syndrome (SIDS) rate following prevention programmes in Australasia, Europe and North America, mainly due to changing infants from the prone sleeping position onto their sides or backs. This report reviews previous SIDS observational studies with data on side sleeping position and bed sharing. The relative risk for SIDS calculated from previous studies for side vs back sleeping position is 2.02 (95% CI = 1.68, 2.43). This result suggests that further substantial decreases in SIDS could be expected if infants were placed to sleep on their backs. With regard to bed sharing, the summary SIDS relative risk is 2.06 (1.70, 2.50) for infants of smoking mothers and 1.42 (1.12, 1.79) for infants of nonsmoking mothers. Public health policy should be directed against bed sharing by infants whose mothers smoke as they carry an increased risk of SIDS from bed sharing in addition to their already increased risk from maternal smoking. For infants of nonsmoking mothers, who have a low absolute risk of SIDS, the 40-50% increase in risk needs to be balanced against other perceived benefits from bed sharing, such as increased breastfeeding.