A survey by telephone interviews has been carried out in 1993 in the canton of Geneva, in order to measure the prevalence of 3 risk factors for the sudden infant death syndrome (SIDS) and to evaluate the potential for SIDS prevention based on these factors: prone sleeping position, tobacco smoking by the parents during pregnancy, and no complete breast-feeding at 8 days of age. 278 families participated to the study, of 320 families who could be contacted by telephone in Geneva, from a random sample of 550 families having had a child in Geneva in the preceding 12 months. 40% of the infants had been put to bed in the prone position on the preceding evening 18% of the mothers had smoked during pregnancy. Prevalence of low birth weight was 4.9% for 0 to 4 cigarettes per day during pregnancy, 17.2% for 5 cigarettes and more. At one week, 16.5% of children were not exclusively breast-fed. On the basis of these results, it can be estimated that an effective prevention programme, centered on prone sleeping position could decrease the incidence of SIDS by 50% or more. An even greater fraction of cases, up to 80%, could be avoided by the prevention of the 3 studied factors. These estimates show the need to develop a mother and child health programme in Switzerland.