Background In order to ensure that legalized abortion in South Africa improves reproductive health, women must know that abortion is a legal option in the case of unwanted pregnancy. This study investigated knowledge of abortion legislation eight years after the introduction of legal abortion services in one province of South Africa. Methods In 2004/2005, we conducted a cross-sectional study among 831 sexually-active women attending 26 public health clinics in one urban and one rural health region of the Western Cape Province. Results Thirty-two percent of women did not know that abortion is currently legal. Among those who knew of legal abortion, few had knowledge of the time restrictions involved. Conclusion In South Africa there is an unmet need among women for information on abortion. Strategies should be developed to address this gap so that women are fully informed of their rights to a safe and legal termination of pregnancy.