In France, the financing of healthcare is characterised by the juxtaposition of reimbursements from compulsory health insurance (AMO) and complementary insurance (AMC). Health expenses to be paid by insured individuals following application of these two levels of cover, constitute the essential indicators of access to healthcare, but these have been little studied to date, due to a lack of adequate national sources. This article aims to fill this gap by using the administrative data of a particular mutual insurance company simultaneously managing AMO and AMC, thus allowing an analysis of charges before (RACO) and after (RACC) application of the complementary insurance. First we studied the level, distribution and concentration of the charges before and after reimbursement by complementary insurance for all outpatient expenses, then per healthcare item. In a second step, we analysed the concentration of charges after application of the AMO and AMC, taking into account two healthcare needs indicators: the fact of being exempt or not from costs, and the level of expenses before reimbursement. In our sample, in 2002, 5% of the population paid RACC of more than 551 euros for outpatient expenses and 1% paid RACC of more than 1,272 euros for outpatient expenses. The RACC of individuals exempt from costs was on average 70% higher than the RACC of those who were not exempt. We show that although the AMO and AMC successively provide a certain amount of mutualisation, they do not reduce in the same way the concentration of charges which may exist for individuals who are the most ill. Thus, for healthcare items which are most often associated with illness and for which there is a certain pricing freedom (for consultations, technical medical procedures and other prescriptions), the mutualising effect of the AMC in 2002 appeared to be relatively low in comparison with that of the AMO.