1. A number of cohort and case-control studies have shown clear, dose-related associations between maternal smoking and infant death. The strongest relationships were found when the mother smoked during pregnancy as well as postnatally. Maternal smoking during pregnancy increases the risk for SIDS in most studies, whereas it appears that maternal smoking only postnatally also leads to an increase in risk. In addition, smoking only by the father appears to increase the risk for SIDS, but this is not seen in all studies. 2. Exposure of children to environmental tobacco smoke (ETS) increases the risk of having night cough and respiratory infections (bronchitis, bronchiolitis, pneumonia), especially during the first 2 years of life. An increased risk is also seen in studies not distinguishing between upper and lower respiratory diagnoses. Long-term breastfeeding may have a protective effect on ETS-increased risk of lower respiratory tract illness. One study of older children reports that ETS combined with allergy increased the risk of acute respiratory tract infections above that due to ETS alone. 3. The number of new episodes and duration of otitis media with effusion in young children is positively correlated with ETS exposure. Especially infants with lower birth weights had a high risk of recurrent otitis media during the first year of life when the mother was a heavy smoker. 4. Passive smoking has been reported as a risk factor in meningococcal disease and tuberculosis in young children.