As the State medical insurance system (Sécurité Sociale) covers 75.8% of healthcare expenditures in France, access to healthcare partly depends on whether patients have supplemental insurance coverage. The government has taken measures to improve access by the lowest-income households to supplemental plans such as Couverture Maladie Universelle Complémentaire (CMU-C) and Aide Complémentaire Santé (ACS). How effective have these programs been in making supplemental health insurance more affordable? Is the persistence of a category of persons with little or no coverage due to financial hardship among the lowest-earning households? Using data from INSEE's 2006 Family Budget Survey, our study describes the distribution of supplemental health insurance by income bracket. We then assess the affordability of supplemental coverage by analyzing the distribution of household expenditures for that purpose. Lastly, we study the determinants of the decision to take out supplemental health insurance and of the expenditure devoted to acquiring it. The results confirm the existence of financial obstacles to accessing supplemental health insurance in France. Supplemental-insurance coverage rates and spending rise sharply with income. Nevertheless, the lowest-income households devote as much as 8.5% and 10.7% of their disposable income respectively tp purchasing such coverage, depending on whether they are insured under an individual policy or via their employers. By contrast, the most affluent households allocate only 2.3% and 3.3% respectively. We may regard supplemental insurance as unaffordable for 18.5% of the total French population and for 10.3% of the population not covered by CMU-C, insofar as its purchase sends such households below the poverty line.