BACKGROUND: Unsafe abortion is estimated to account for 13% of maternal mortality globally. Medical abortion is a safe alternative. METHODS: By estimating mortality risks for unsafe and medical abortion and childbirth for Tanzania and Ethiopia, we modelled changes in maternal mortality that are achievable if unsafe abortion were replaced by medical abortion. We selected Ethiopia and Tanzania because of their high maternal mortality ratios (MMRatios) and contrasting situations regarding health care provision and abortion legislation. We focused on misoprostol-only regimens due to the drug's low cost and accessibility. We included the impact of medical abortion on women who would otherwise choose unsafe abortion and on women with unwanted/mistimed pregnancies who would otherwise carry to term. RESULTS: Thousands of lives could be saved each year in each country by implementing medical abortion using misoprostol (2122 in Tanzania and 2551 in Ethiopia assuming coverage equals family planning services levels: 56% for Tanzania, 31% for Ethiopia). Changes in MMRatios would be less pronounced because the intervention would also affect national birth rates. CONCLUSIONS: This is the first analysis of impact of medical abortion provision which takes into account additional potential users other than those currently using unsafe abortion. Thousands of women's lives could be saved, but this may not be reflected in as substantial changes in MMRatios because of medical abortion's demographic impact. Therefore policy makers must be aware of the inability of some traditional measures of maternal mortality to detect the real benefits offered by such an intervention.