OBJECTIVES: In low- and middle-income countries medicine costs account for a substantial part of total health care costs (WHO estimate: 25-70%). In these countries many patients pay for medicines out-of-pocket. This study’s aim was to calculate the affordability of four essential medicines (salbutamol inhaler (100mcg/dose), glibenclamide (5mg), atenolol (50mg) and amoxicillin (250mg)) for 17 low- and middle-income countries. METHODS: Previous research expressed affordability of medicines in the number of days’ wages of the lowest paid unskilled government worker. Using medicine prices from a joint project between Health Action International & WHO, and expenditure data and income distributions from the World Bank, this study applied a more common measure of affordability of medicines based on impoverishment (i.e., percentage below US$1 or $2 per day after medicine procurement). Affordability is calculated for Originator Brand (OB) and Lowest Priced Generic (LPG) medicines in both the public and private sector. RESULTS: OB medicines are less affordable than LPG medicines. Impoverishment rates (IRs) between OB and LPG medicines vary substantially; 10.8% vs. 4.0% (OB vs. LPG below US$1, public sector atenolol, Philippines). IRs of up to 33.6% were found (below US$1, OB private sector amoxicillin, Indonesia). IRs in low-income countries are lower than in middle-income countries due to high numbers already living below US$1 or $2 per day. We distinguish between those being impoverished and those for whom medicines are unaffordable in the first place (i.e. below US$1 or $2 before medicine procurement). In the public sector IRs are lower than in the private sector but availability of medicines is low. CONCLUSIONS: In low- and middle-income countries medicine prices in relation to available income are such that obtaining necessary medication will impoverish large numbers of people. These results call for action by politicians, policymakers, and civil societies.