Official statistics on smoking during pregnancy in Scotland are drawn from SMR02 data that are collected at a woman’s booking visit during the first trimester of pregnancy. The report presents findings from a re-analysis of these data for Scotland as a whole and Glasgow in particular. The analysis showed that reductions in smoking rates, particularly in more disadvantaged areas, were not due to women giving up smoking. Instead, the proportion of women whose smoking status was recorded as ‘not known’ rose significantly in the period 1995-2005 (by one third) across Scotland, with the problem being most acute in Glasgow, where the percentage of ‘not known’ cases trebled between 2000 and 2005.