This article considers the methods used to estimate the number of abortions before the 1967 Abortion Act came into operation. It suggests that the registration of legal abortions has enabled a new method to be used to calculate the number of illegal operations. The article concludes that the major effect of the Act was to transfer abortions from the illegal to the legal sector and, using the new method of calculation, estimates a total number of abortions immediately before the Act (...) of just over 100,000 a year. (shrink)