Asthma is the most common and potentially serious medical problem encountered in pregnancy. The prevalence of asthma during pregnancy is generally quoted as being between 1% and 4% which is much lower than general population estimates. The aim of this analysis was to estimate the prevalence of asthma and smoking during pregnancy; and to describe the relationship between the two. A cross-sectional random sample survey of recently delivered Western Australian mothers was carried out in 1995 and 82% of mothers responded. In total 21.3% of women reported ever having asthma at some stage in their life and 12.4% currently had asthma. These results are consistent with general population estimates. Overall 22.7% of women smoked at some stage in pregnancy, which is consistent with the limited comparison data available. Current asthmatics were more likely to smoke during pregnancy than non-asthmatics, although this difference was not statistically significant. Continued vigorous efforts are required to discourage all women and girls from taking up smoking and to encourage those who smoke to quit. This is particularly pertinent for asthmatic women who are pregnant or planning a pregnancy.