The paper examines smoking amongst a sample of 1248 women giving birth to live-born infants. The findings show: 1. That about 26 percent of women smoked throughout pregnancy and a further 8.0 percent smoked at some time during pregnancy. 2. Smoking during pregnancy was realted to the mother's social background: younger mothers, non-European mothers, mothers with no formal educational qualifications, mothers of low socioeconomic background and mothers of ex-nuptial infants tended to smoke more during pregnancy. 3. Smoking was associated with a decrease in birth weight, a greater risk of low birth weight (less than 2500g) infants and a greater risk of spontaneous abortion. There was no statistically significant relationship between smoking during pregnancy and: the risk of complicated labour, time to the onset of neonatal respiration, the use of active resuscitation or the risk of neonatal infection.