The cost of antiretrovirals is borne by donors in many low- and middle-income countries, including St Lucia. Although donor involvement has facilitated access to antiretrovirals, donor engagement in HIV/AIDS has changed over the years. This paper assesses the affordability of antiretrovirals at the individual level if donors were no longer available to fund the cost of first and second-line antiretrovirals and a prospective third-line regimen. Various conceptions of affordability are reviewed using different assumptions of what is required to maintain a standard of living that would avoid individuals descending into poverty as a result of antiretroviral purchases. These concepts of affordability are operationalized using data from the Household Budgeting Survey conducted in St Lucia in 2005/2006. While there is a range of results for the affordability of first and second-line antiretrovirals depending on which standard of affordability is used, third-line antiretrovirals are unaffordable to more than 80% of the population across the four standards of affordability used – the national poverty line, 50% of median annual consumption, 10% of annual consumption and a proposed reasonable minimum standard.